Many theorists predict that employers will eventually adapt and absorb this army of boomers who either desire or need to remain on the job at ages when their parents were working on their golf strokes. But there are other needs, too. "Whatever economic challenges the over-65s are facing these days, they pale by comparison with the money troubles of the young," writes Paul Taylor of the Pew Research Center in the new book The Next America: Boomers, Millennials, and the Looming Generational Showdown. Staggered by a slow economic recovery and their hefty college debts, today's younger people are going to need all the help they can get.

Often, they are finding that assistance from boomers: A 2013 Merrill Lynch–Age Wave survey found that 62 percent of those 50 or older had helped out family members financially in the past five years. Other boomers are pitching in with unpaid labor: Currently 30 percent of preschoolers are taken care of by grandparents when Mom or Dad is at work or school.

So there is meaningful work aplenty. Even if boomers wanted to amble off to the fishing hole for the remainder of their years, the rest of us can't afford to let them: We still need them here.

And this is an apt thing, in many ways. "Boomers want to be where the action is," Dychtwald says — and they'll get their wish. "I don't think all 78 million boomers are going to have an easy and carefree time of it. I do think we will make it a more robust and interesting period of life than we have to date."

But there's also a danger of creating unrealistic expectations for older adults, says Marty Martinson, professor of health education at San Francisco State University. "It's one thing to say we need to create communities where elders are part of the fabric of what is going on," she says. "But we've constructed this idea of the 90-year-old surfer-volunteer as the ideal retiree." Yes, older people want to be active, useful parts of society, Martinson is quick to add. But this should be a choice, not an obligation.

There is something to be said for Martinson's take. If we once implied that older Americans had a duty to go off and enjoy themselves, we're now risking expecting the exact opposite — that they have responsibility to the rest of us.

No wonder "retirement" no longer seems like the right word to describe this strange new time. The idea of having a life after leaving the workforce barely existed a century ago; today, it's an institution. As circumstances change, so will what we think we want from this still-evolving life stage. It's going to be a work in progress for a long time.

And that's a good thing. For a generation that has always defied expectations, this last act will be one to watch.

Helaine Olen is the author of Pound Foolish: Exposing the Dark Side of the Personal Finance Industry.

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