This was back when people over 65 accounted for a relatively small proportion of the US population — under 10 percent in 1960, according to the census from that year — and the average age at the time of death hovered under 70. Since then, advances

in medicine and increasingly widespread health-consciousness have caused these numbers to rise precipitously. Demographers predict that by 2030, average life expectancy will have climbed past 80 and people over 65 will account for more than 20 percent of the country’s population.

Taken together, these changes amount to a dramatic transformation of American society that has only just begun — one that promises to have acute ramifications for the composition of our families, the makeup of our workforce, the functioning of our health care system, and even the layout of our cities. As America grows increasingly gray, the needs and desires of the elderly will become a more important and more visible part of the culture — and the years after age 65 will account for an increasingly large portion of our lives.

Plenty has been said about how old age is changing now. But what will it be like for those of us who won’t be hitting our 50th reunions for several more decades? Amid all the demographic projections, and all the worries about resources, we tend to assume that the actual texture of life as an old person in the future will be more or less what it is today — that even as old age lasts longer and becomes more prevalent in society, the concept itself, and the kind of life one associates with it, will remain intact. But this is a failure of imagination: In fact, old age in the future — particularly if you’re looking at 2050 and later — promises to bear little resemblance to old age as it is experienced in 2011.

Predicting trends in aging and preparing people for the changes ahead has become something of a cottage industry in recent years. Much of this takes the form of marketing and advice literature written by gurus promoting the so-called new old age. But there is also more serious work being done, both in academic settings like the MIT AgeLab and Stanford Center for Longevity — where researchers are studying new technologies, products, and policies geared towards making old age a less limiting and more fulfilling time in one’s life — and in private organizations experimenting with new models for how seniors with chronic illnesses might receive the care they need without being institutionalized. The American Society on Aging recently published a special issue of its journal Generations, devoted to the future of aging, and two weeks ago gathered researchers and care providers at their annual conference in San Francisco for a daylong symposium on the subject.

When these experts look ahead, they see a population of people who are less vulnerable to isolation, less likely to be bored, and more adept at using technologies to stay healthy and compensate for various ways in which life has become more difficult. They also see a population less inclined to leave the workforce — or less able to leave it — for a life of pure leisure: “Retirement” in today’s sense is likely to shrivel and be pushed later into life.

“We’re looking at people living 30 to 40 years longer than they did 100 years ago,” said Joseph Coughlin, director of the MIT AgeLab. “More of your adult life will be lived after the age of 50 than before age 50. The question is, what’re you going to do with it?”

There are still unknowns, such as how and whether America will keep funding the health care system the old now count on, or whether the prevalence of dementia will continue to grow or be vanquished by medicine. And skeptics warn against fantasies of Peter Pan-style agelessness: There is no escaping that age changes how you move and how you think. But among the most resonant — and least obvious — points that aging experts make is that old age, though a constant throughout human history, does not refer to some static set of habits, joys, and frustrations. Rather, it is an evolving condition that is continuously defined, and redefined, with every generation that experiences it.

Old age as we know it today owes much of its shape and character to a single decision the government made in 1935, when the Social Security Act set a mandatory retirement age of 65. “There was actually a theory, called ‘disengagement theory,’ that said it was mutually beneficial for older adults to remove themselves from active, productive roles in society,” said David Burdick, director of the Stockton Center on Successful Aging in New Jersey.

That idea was a product of its time. Medical breakthroughs had sent infant mortality rates down and life expectancy up, and older workers were competing with a lot more young ones for jobs. The retirement system, according to Burdick, was essentially designed to ease these obsolete old people out of the workforce to make room. And even though retirement eventually ceased to be mandatory in the United States, the Social Security Act left behind a potent legacy in marking 65 as a fault line in the public imagination between those whom our society values and those it considers no longer productive.

That fault line has started to fade in recent years, as more and more 65-year-olds elect to stay in the workforce either because they haven’t saved enough money to retire or because they just don’t feel like quitting yet. The next decade will see the line blur even further, as millions of baby boomers start reaching the line that marked the end of their parents’ careers and blowing right past it.

“You look at surveys of baby boomers, something like 80 percent of them say they want to continue working after the age of retirement,” said Richard Adler, an affiliate of the Palo Alto nonprofit The Institute for the Future, who helped organize the symposium on the future of aging at last month’s conference.

All told, by the time the boomers are done with it, old age is likely to be a very different beast than when they found it. Some, like Marc Freedman, author of a recent book on aging called “The Big Shift,” argue that a new life stage will have emerged. Just as adolescence became a household concept in the early 20th century that was shorthand for a whole set of behaviors, desires, and difficulties, so too will this as-yet-unnamed period — starting somewhere around 55 and continuing roughly through one’s mid-80s — become synonymous with a particular mode of life, a sort of second adulthood during which a person is not only active and autonomous but motivated by new professional and personal goals. It remains to be seen whether our nation’s marketers will succeed at inventing a catchy new term to describe it.

Certain changes that age brings are unavoidable: Every generation can expect its knees to become creaky, its eyesight less keen; even very active seniors leave the house less than they once did. One reason experts foresee a more autonomous future for older people is that technology — now often seen as a cultural line that separates the oldest Americans from their younger counterparts — will increasingly integrate into people’s lives in a way that makes everyday tasks easier, not more confusing.

Some of this technology relates to health. The old need a different kind of care than younger people — steady monitoring rather than occasional trips to the doctor — and there are devices being tested in pilot programs around the country that keep a constant eye on people’s vital signs from their homes and remind them to take their medication. If you’re old, quick detection of an abnormality — a weight change from fluid buildup, a refrigerator door that can tell you haven’t been eating, even a keyboard that can tell you’ve started typing more slowly than you used to — can save a costly and dangerous trip to the hospital later.

“Many of the problems of aging are evanescent — they come and they go,” said Tracy Zitzelberger, the administrative director of the Oregon Center for Aging and Technology at Oregon Health & Science University, which is developing a number of monitoring devices. “There are good days and bad days. When we only see our doctors on a good day because that’s when we don’t cancel our appointments, we get a very skewed assessment of our functioning. And that doesn’t get at the heart of the challenges of aging.”

The smarter our houses get, the thinking goes, the longer we’ll be able to stay in them — watched passively and remotely by nurses and family long after the point where today we’d end up in a nursing home.

Such pervasive monitoring may sound almost Big Brother-ish to someone who grew up in a world without it, but the 80-year-olds of the future won’t be those people — in fact, the hyper-networking of their homes will seem like just an extension of a life where one’s personal devices have long held and transmitted seemingly private information for the purpose of making life easier. And that’s where the cultural shift comes in: The baseline assumptions of future old people won’t be those of people who grew up in the 1940s, or even the 1960s. They’ll be shaped by people who came of age texting their friends, allowing their phones to track their whereabouts, and expecting to be generating — and receiving — information all the time.

“Younger generations are much more proficient in navigating this gray line between the physical world and the virtual world, and they’ll continue that as they age,” said George Demiris, an associate professor of biobehavioral nursing and health systems at the University of Washington.

In that sense, one of the key struggles that people face in old age — isolation and boredom — is likely to look very different in the future, if not vanish entirely for some. The people who will be facing these challenges in 40 years will be people accustomed to amusing themselves digitally, and creating a social life for themselves without another person physically present. To put it bluntly, the people who turn 70 in the year 2050 will be people who grew up playing video games. And the digital environment that now seems like a recipe for distraction — a constant feed of personal messages, links, and updates on one’s friends — starts to look a lot like a way for even a housebound person to stay engaged with the world.

This will do more than just give old people something to do — it also promises to have a significant effect on the perceived role of elderly people in society, keeping them connected to the working world for longer, and restoring some of the buying power they would have forfeited as retirees. This is part of the so-called e-Quality Theory of Aging proposed by Douglas McConatha at West Chester University in Pennsylvania. Instead of letting technology marginalize the elderly the way it did following the industrial revolution, he says, we can expect it to have a positive impact this time around, restoring elderly people’s social status by sharply reducing the number of things they can’t do and by giving them back some of their influence in the market.

There are at least two major issues looming over this happy, sunny future: the fact that 43 percent of people over 85 show symptoms of Alzheimer’s disease, and the possibility that the most promising changes up ahead will only be within reach of those who can afford them. There are those — see Susan Jacoby, author of the recent book “Never Say Die: The Myth and Marketing of The New Old Age” — who argue that any discussion about the future of old age that fails to take these issues into account is an exercise in science fiction, and even propaganda.

It is extremely difficult, if not downright impossible, to predict how these tough issues will unfold down the line. Dementia is a focus of much medical research, but so far there is little evidence that a cure is possible. And the affordability of retirement — the extent to which the 20th-century benefits contract with old people will survive — is ultimately an issue that has to be worked out politically. To the extent that it depends on postponing benefits and rationing health care for retirees, that question will be harder, not easier, to solve as the politically powerful boomer generation fills out the ranks of retirees.

Does such uncertainty mean that young people shouldn’t even try to imagine what old age will be like? Or does it mean the opposite — that we should try to nail down what we can, and brace ourselves for the rest? Because for all that stands to change politically and technologically in coming decades, one thing we can definitely count on is that the old people of the future will have been young once — and the lives they were accustomed to then will, more than anything else, determine the lives they expect to lead later. Here’s hoping the iPad 15 plays cat videos.

Leon Neyfakh is the staff writer for Ideas. E-mail lneyfakh@globe.com.