After retiring as a pediatrician at 65, Bertram Koel returned to school to earn a master’s degree in public health. For more than 10 “very fulfilling” years, he used both his new degree and his former skills as an advocate for children on the policy level. In his mid-80s, he retired a second time and began looking for a place to take classes.

Eight years ago at 86, Koel enrolled in the Osher Lifelong Learning Institute at San Francisco State University. Probably the oldest student at OLLI, Koel has been an avid supporter of the program. These days, and formerly with his late wife, Renee Golanty Koel, he has attended almost all of the writing classes, and gladly shared excerpts of his work at OLLI creativity events.

At a time when people who retire at 65 may live another 20, 30 or more years, many vital, robust seniors make up today’s aging population. However, after the first months of leisure following decades of deadlines and pressures, the prospect of unlimited free time can quickly become oppressive for retirees.

What to do with the rest of your life? For those who have experienced — or who want to experience — joy in learning, classes are a popular option. This time around, though, they choose subjects they want to learn, at their own pace, preferably without exams and papers.

A 2003 grant from the Bernard Osher Foundation to San Francisco State University led to the creation of the Osher Lifelong Learning Institute at San Francisco State University, one of 118 U.S. institutes of learning for older adults funded by the Osher foundation.

The institute offers year-round classes and other events at S.F. State’s downtown campus at 835 Market St., and on the main campus at Holloway and 19th avenues. Current and retired S.F. State professors and others (such as J. film critic Michael Fox and J.  seniors columnist Barbara Brooker) teach classes, which average around 30 students. Jewish-themed classes, such as this summer’s “Eastern European Jews” and last summer’s “Jewish Communities: Remote Places,” are not uncommon.

Fall classes begin Sept. 8.

“We’re a membership organization,” said OLLI director Sandra Halladey. “Our members have a lot of say in what we offer.” Active volunteers on the curriculum and outreach committees support the nine-member governing council, elected by fellow OLLI members. Members put on tours, lectures and special events. The member-facilitated Caring Community Study Group, which has met for more than six years, supports members through the difficult challenges of aging and loss; a world affairs discussion group has an equally long history. “I may be the director, but OLLI wouldn’t exist without the energy and involvement of its members,” Halladay said.

The most popular classes are in the humanities and writing, she added, noting that at least one writing class is offered in every session.

Michele Praeger enrolled in OLLI seven years ago after retiring from U.C. Davis as a professor of French and moving to San Francisco. After taking writing classes at OLLI, Praeger and other writers formed a writers’ circle for mutual support and criticism. A longtime member of the curriculum committee, Praeger, 67, is an advocate for OLLI’s community of writers. “It’s a lot of work trying to put these classes together,” she said. “Lecture classes are not popular at OLLI. We want instructors who value students’ experiences and are comfortable learning from them.”

Diane Ringel, 65, likes exploring new places. After taking early retirement, Ringel sold her house in Los Angeles and moved to St. Thomas, Virgin Islands. “It was a good life,” she said. “I loved the weather and was very active in the synagogue, the second oldest in the Western Hemisphere. But after a while I became acutely aware of how lonely my father and his friends were who had moved to Florida for the weather. Being near family becomes more important as you age.”

Because her two sons live in San Francisco, Ringel purchased a 110-year-old Victorian in the South of Market area. Then she moved on to the next task: finding friends.

On a visit to her father in Boca Roca, father and daughter took an adult education class in Russian opera. “The class was great,” Ringel said. “When I moved to San Francisco and saw an ad for OLLI at San Francisco State, I immediately registered. I take two classes a session: one on a topic I know something about and one on an area I want to explore.”

Soon after entering the program, Ringel approached Halladey with plans for a new interest group: San Francisco adventures. “I pick places that are free and people don’t generally know about,” Ringel said. “I did a lot of international travel when I worked, so I’m comfortable exploring new places, but it’s always better when you do it with other people.” Twenty-five members participated in the group’s tour of KQED.

A recent curriculum forum led to offering classes that tie in with anniversaries and cultural activities. A class on the causes and consequences of World War I and another on the 2014-15 San Francisco Symphony season are scheduled for the fall session.

Peter Susskind, a former assistant conductor and popular pre-performance lecturer at the San Francisco Opera who taught an OLLI class on the opera, will teach the course on the symphony. “I like teaching here,” he said of OLLI. “Students are my age. Most important, they want to be here; it’s not the elective they’ve got to take. There’s a lovely range of views and opinions. Some of them are very knowledgeable about music.”

It was “a little easier with the opera classes, because there were only a limited number of operas [in the San Francisco Opera season], in contrast to 23 weeks of performances with many visiting orchestras,” Susskind added, taking a break from selecting and downloading the excerpts he will present. “I’m also arranging to bring in at least one visiting performer and am working on getting half-price tickets for students to attend the symphonies linked to the classes.”

Fall courses also look at local politics, documentary film (taught by Fox), art and other topics. In the planning stages are classes that tie in with exhibits at S.F.’s Contemporary Jewish Museum, according to Halladey.

Beyond the classes themselves, for seniors who become members of OLLI it’s about more than studying interesting subjects, according to Koel. “At OLLI, I became a writer,” he said, “and OLLI became the place where [my wife and I] made many of our best friends, and the setting in which we developed our creativity.”

Fall classes at the Osher Lifelong Learning Institute at San Francisco State University begin Sept. 8. For information, call (415) 817-4243 or visit www.olli.sfsu.edu. OLLI classes are also offered at U.C. Berkeley, California State University East Bay and Dominican University in San Rafael. In addition, the Fromm Institute at University of San Francisco and City College of San Francisco offer older adult programs.