HUDSON, Mass. — The condominium that retirees Richard and Mary Jean Ebens bought three years ago for $305,000 has some nice amenities: 2,000 square feet of living space, a garage, a basement, a deck looking over the garden, and a reasonable 45-minute drive to Boston.

But the social benefits are what make it special to Richard, 75, a former Episcopal pastor, and Mary Jean, the 69-year-old former operations manager for a computer company. That's because The Villages at Quail Run, the 150-unit "active adult community" the Ebens call home, is for people 55 and older.

Age-restricted developments — which typically lack the medical care and services available in nursing homes and assisted living facilities — expanded in the 1990s in Sun Belt retirement havens after Congress granted developers exemptions from federal housing anti-discrimination statutes.

Thanks to accommodating local zoning rules and officials' desire to attract older residents who aren't a drain on the tax base, the projects are becoming increasingly common outside the Sun Belt, particularly in expensive housing markets in the Northeast. But some housing advocates claim it's edging out young families and others from the housing market.

"Now you're seeing a boom going on all around the country," said Jeff Jenkins, assistant director of 50-plus housing for the National Association of Home Builders. About 60 percent of such developments are now outside the Sun Belt, with the growth in northerly states driven in part by many buyers' wishes to stay closer to family and the communities where they spent their working lives, he said.

The number of projects has grown over the past decade to about 1,250 in 44 states, according to a private database, the National Directory of Lifestyle Communities. More than six times as many new projects were opened for sale in 2004 (99) compared with 1995 (15), with 74 percent of the communities built last year constructed outside the 13 Sun Belt states.

Developers are responding to the aging of the 78 million baby boomers born from 1946 to 1964. Active adult housing accounted for one-third of the 38,612 homes built across the nation last year by Pulte Homes, compared with one-quarter of its home production in 2001.

"We don't see any end to the active adult boom in sight," said Richard Dugas, chief executive of Bloomfield Hills, Mich.-based Pulte, the nation's largest builder of active adult housing.

But some affordable housing advocates in high-cost areas question whether age-restricted housing is growing too fast to meet market demand and taking up too great a share of new construction.

Although Richard Ebens embraces the trend, he worries the glut of adult communities will force out young families struggling to buy into a market where the construction is limited by strict zoning and shrinking tracts of available land. In Hudson, a bedroom community of 18,000 people west of Boston, 474 of the town's roughly 7,000 housing units are in age-restricted complexes.

"We are an aging population, so these projects serve a need," Ebens said. "(But) I frankly don't understand how young families can afford a house these days."

On a national scale, there has been no large movement against such projects, said Brian Green, a fair housing policy director for the U.S. Department of Housing and Urban Development.

"There is a general awareness that some communities prefer elderly housing to affordable housing for families, but we haven't been petitioned in any way about the need to decrease the amount of that type of housing," Green said.

But the pressure is already being felt in Massachusetts, where housing prices have seen the steepest price increase in the nation over the past 25 years, rising 516 percent from 1980 to 2004, according to federal data.

Already, several age-restricted projects in the state remain partially vacant — in some cases leading developers to ask that age restrictions be lifted.