It's never too late to go to college, especially when you don't have to worry about your GPA.

A growing number of older Americans are doing just that, and many schools are going to extraordinary lengths to accommodate them.

Throughout the United States, universities and colleges are creating or planning housing for seniors -- as in the elderly -- on or near campus. Experts estimate there are upwards of 50 university-linked retirement communities already built and 30 more planned.

"There are a wide variety of experiments being tried in this area," said Gerard Badler, managing director of Campus Continuum, a Newton, Mass.-based senior-housing research firm.

Some communities feature single-family homes; others are built around garden apartments. Some feature nursing-home units for the totally dependent; others are for the strictly independent. Some are closely affiliated with a university; others are simply near one.

They're located in almost all parts of the country, from the University of Michigan to the University of Florida-Gainesville, from Penn State University to the University of Arizona, and parts in between, such as Notre Dame in South Bend, Ind.

The schools are motivated partly by demographics. In the face of falling enrollment of traditional college-age students, universities see retirees as a growing market for their services.

The allure is both the intellectual and cultural stimulation a college campus can provide, said Mark W. Fagan, head of the sociology and social work department at Jacksonville State University in Alabama. "College students and retirees look for the same thing -- a good time."

But the colleges also have another motive -- potential future donations to university endowments. Many are wooing retired faculty and alumni who might return and then someday bequeath a large gift, or give a bigger one than they might have otherwise.

Notre Dame, for instance, already received $1 million from a resident of its retirement community. The builder of a gated-retirement community at Georgia Tech is soliciting 100,000 alumni to buy into a $66 million, 600-acre golf course community featuring 206 homes on $240,000 lots.

Colleges also see a chance to bolster current revenue and the local economy. The Georgia Tech community, once completed, will generate an estimated $1 million a year for that school's athletic and alumni associations. University-linked retirement communities create 2.5 jobs for every retiree, experts said.

With average assets of $370,000 and $41,000 in average annual income, each retiree household has the same economic impact as 3.7 factory jobs. What's more, seniors in university-linked retirement communities tend to pay more in taxes than the cost in services. "It's the only population group that does that," Fagan said.

Seniors who return to campus can generally audit classes for free, but most university-linked retirement communities carry a hefty price tag, often called an entrance fee. Campus Continuum's Badler said the fee averages about $200,000, a portion of which is usually returned to the resident's estate, along with an average monthly fee of $400.

Lasell Village is a Boston-area community linked to Lasell College and its 1,500 full-time students. Its condo prices range from $250,000 to almost $800,000, with monthly fees of about $2,000.

At present, the average Lasell Village resident is 82 years old and is taking a required 450 hours of learning a year. Unlike Georgia Tech's planned community, Lasell Village has no golf course. Also unlike Georgia Tech, Lasell Village has a nursing home.

One cautionary note: These housing units aren't necessarily a good investment, since the property owners may retain any increase in the value of the property above the purchase price.