Instead, older homeowners often move to rentals where people of all ages live. Among those 90 and older, about 33 percent rent in an all-ages neighborhood, compared with 17 percent of those 55 and older, according to a study by the National Investment Center for the Seniors Housing & Care Industries.

"A lot of people really do move out of their homes" to rent in all-ages neighborhoods, said Robert Kramer, president of National Investment Center, a nonprofit research group that analyzes the senior-housing industry for investors.

"Between ages 55 and 90, you're seeing almost a doubling in the percentage of those who are renting (in all-ages neighborhoods) versus owning," he said, though in absolute numbers the sample size is smaller for the 90-plus age group.

By contrast, about 5 percent of people in the 90-and-older group rent in senior housing that offers age-specific services.

Cost is one reason senior-centered housing is avoided. Whether it's an active-adult community for those 55-plus, an assisted-living center that provides meals and other services or a continuing-care community offering nursing-home care, it's likely to cost more than a small apartment in an all-ages area.

"It's fair to say that we need to do a better job in this country in providing these housing options across all affordability levels," said Elinor Ginzler, manager for independent living and long-term care at AARP. "We have some. We don't have enough."

But the choice is not always driven by cost: Some retirees shun senior housing because it continues to connote a place where only the infirm live. "There's the old perception of a nursing home, where you go there to die, or at least the perception of 'I don't want to be around a lot of people who are infirm,' " Kramer said.

Those perceptions may change after visiting senior-focused housing, he said. "Our studies show that once people know someone living in one or once they've visited one they're far more likely to move to one."

And, as baby boomers age, it's likely those perceptions will be nudged in a different direction by industry marketers. In the future, the words "retirement" and "seniors" will be eliminated from advertising, Kramer predicted. "Baby boomers don't want to think of it as retirement and they don't want to think of themselves as seniors."

About 4 million older Americans live in age-qualified housing, from assisted-living facilities, where people move in their early 80s on average, to age-restricted "active living" communities where the average move-in age is mid-60s.

For some retirees, it's not a negative view of senior housing that keeps them away. They simply like the benefits of all-ages neighborhoods. "There are people who say 'I don't want to live with all people of the same age. I like living next door to a family with young children,' " Ginzler said.

Still, more seniors report being happier in age-qualified housing than those who stay in their own homes in an all-ages neighborhood.

Ninety percent of those in a retirement community said they were happy "much of the time" during the last week, versus 83 percent of those in their own homes, according to the NIC study, which analyzed data from the University of Michigan Health and Retirement Study of more than 13,000 households.

"There is no question but that there are some older citizens who end up isolated in their homes. An age-qualified housing setting can mean more social stimulation," Ginzler said. "The degree to which one feels engaged with others can have a huge impact on your health status, not just your mental health," but physical health also, she said.

Still, "housing (is) an incredibly individualistic factor in people's lives," she said. "I tend to shy away from generalizations such as older people are better off in 'fill in the blank.' Older people are as broad in the way they live their lives and want to live their lives as younger people."

While 75 percent of Americans aged 45-and-up say they'll be able to stay at home for the rest of their lives, about half think they'll need to make changes to their home to make that possible, according to an AARP survey earlier this year.

That may not be entirely realistic. Climbing the stairs regularly may become less of an option, and it may get harder to get in and out of the bathtub. If you're remodeling your bathroom now, make the future addition of grab bars easier by reinforcing the walls, Krueger said.

When painting the house, consider making a strong contrast between walls and floors, so "if you have bad eyesight you can actually see clearly where the edge of the wall ends and the floor begins," reducing the risk of falling, Krueger said.