Evelyn Nef decided to give herself a flat stomach for her 80th birthday. So she signed up with a personal trainer. Five years later, Evelyn still exercises regularly.

Unusual for most people, perhaps, but Evelyn Nef is not most people. In the 1940s and '50s, she went on polar expeditions with her second husband, noted explorer Viljhalmur Stefannson, wrote three books about the Arctic and freelanced for the New York Times. At Dartmouth College, whose Baker Library holds the Stefannson Collection, she lectured on polar research.

At age 60, when most people contemplate retirement, Evelyn became a certified psychotherapist and started a 20-year career. "I got my first Social Security check and graduated at about the same time!" she says.

At 80, Evelyn left the therapy field and began her autobiography, which she recently sent to her publisher. Now, several months from her 86th birthday, she contemplates what to do next. Get a job? More traveling? Recently, Evelyn traveled to South America, where she was able to visit "Machu Pichu, Easter Island, and other places I needed to see."

"I'm still very active, physically and mentally and emotionally," Evelyn says, stating the obvious. Her advice to others? Get moving.

"Exercise is a necessity for older people, and younger people as well. It's an antidepressant. It's also free, and non-toxic."

Other advice from Evelyn? Exercise your brain as well as your body. "You have to be involved with something. Volunteer at a hospital, read to somebody, find something so you have to get up and get out of the house. Even if you don't like it, do it. Get interested. Move. Your life depends on it."