In the 10 years that Jacob Cohen, 70, has been retired from teaching, he has taken more than 100 courses at the University of North Carolina—Asheville, averaging three or four a semester. One of his favorite classes was about the history of life on earth, taught by a retired biology professor. He's also taken classes on aging, science and history.

Cohen finds taking classes in retirement to be a challenging way to spend his time. "I always find six or eight (classes) that pique my interest," Cohen says. "I end up with three or four. I like how I feel when I'm being mentally stimulated."

Cohen lives in Asheville, North Carolina, where he can take advantage of the classes for those age 55 or older at the Osher Lifelong Learning Institute at UNC Asheville. The UNC Asheville Osher Lifelong Learning Institute offers some 350 non-credit classes a year for seniors. With a $25 membership fee, the fall and spring semesters are eight weeks and cost $115. The winter and summer semesters are six weeks and cost less, says Catherine Frank, executive director of the Osher Lifelong Learning Institute at UNC Asheville. Subjects range from hands-on arts and crafts to movement and fitness to intellectually challenging current affairs, political science, literature and science classes. Almost all the instructors are volunteers, and the program usually teaches 1,000 students a year, Frank says. The average age is 68, but students as old as 90 take the classes.

Seniors who stay active mentally may be able to help keep their mind sharp longer. "When it comes to brain power, much like your muscles, the 'use it or lose it' concept applies," says Dana Anspach, CEO and founder of Sensible Money in Scottsdale, Arizona. "Retirees who engage in life-long learning keep their brain engaged by challenging themselves to learn new skills. It's important to find things you're curious about and dive in. And in retirement, you have the time to do it."

Taking classes in retirement can also be a way to meet new people with similar interests and socialize. "You can go lots of places to learn. You can purchase CDs or DVDs. You can learn from great teachers," Frank says. "We have a sense of community. You will meet people in classroom and continue conversing after class. We're all teaching and learning together."

The Bernard Osher Foundation supports 122 lifelong learning programs on university and college campuses across the country. There is at least one in each of the 50 states and the District of Columbia. Even if there's not a program near you, many public and private universities offer classroom opportunities to retirees over 60 at little or no cost.

Some colleges, including Pennsylvania State University and Colorado State University, allow seniors to audit classes tuition-free. Other universities, such as Boston University and Georgetown University in the District of Columbia, charge a flat fee to retirees who audit classes, such as $50. Many state university systems, including California State University and the University of Maryland, allow retiree residents above a certain age, usually 60 or 65, to take for-credit classes, typically on a space available basis. Some universities offer online courses for seniors at no or minimal costs. Community colleges may also offer low- or no-cost programs for retirees.

Psychiatrist and consumer health expert Janet Taylor says people who continue to learn in retirement are among the most content and happy. "Those who are lifelong learners realize that just because you are retired or over a certain age doesn't mean you don't want to continue to learn and grow," Taylor says. "Those that are active, read books, go on field trips or always discovering seem to be happy in retirement."

Retirees are free to choose diverse and interesting topics of study that suit their interests. "I've seen retirees take up cooking classes, wood-working, guitar-playing and in a few cases go through financial educational programs like the certified financial planner or retirement management advisor courses," Anspach says. "I have a retired attorney client who went through the same RMA (retirement management advisor) coursework that I went through. He didn't want to manage his investments in retirement, but he did want to learn enough to be able to hire someone that was applying a solid process."

Dan Beerman, 71, and his wife, both retired social workers, were excited at the opportunity to take classes at the OLLI program when they retired to Asheville from Greensboro, North Carolina. "I was shocked when I saw the range of opportunity, from yoga to foreign affairs to music and art and travel. It has a nice range," Beerman says.