Bengie Santos spent 30 years as a dancer and choreographer before deciding she was not ready to stop. At 72, she has been teaching fitness classes at the YMCA of Greater Seattle, a nonprofit community fitness organization, for 14 years. Her students, many of whom are in their 80s and 90s, come several times a week to stretch, dance, and lift weights together.

Some of Santos' students say that younger instructors are great, but don't always understand their needs in the same way. Kerry Ashby, a program executive at the YMCA, says the organization actively recruits instructors from within its older adult classes. "We know it's more than just fitness for the majority of our active older adults," Ashby said. "It's also the mental and emotional aspect."

Experts agree that staying active and connected to others is key to healthy aging, but motivation can be a challenge. Daniel E. Lieberman, an evolutionary biologist at Harvard University, says that finding someone to help you get moving — whether a friend or an instructor — is one of the best ways to overcome that resistance.

Harry King, an 83-year-old personal trainer, echoes that view. "At my age, if I can exercise, why can't other people too?" he said.

Santos says she always thinks about her students when choosing music for class. "I always tell other instructors it isn't your class, it's their class," she said.