Ron Levitt could have retired 16 years ago when he sold his bustling optometry practice in Rocky Hill, Connecticut. Instead, he kept his white coat on, found two part-time gigs seeing patients and continued working.

Today, at 74, Levitt spends all of the money he earns on vacations with his wife and golf-club memberships. Aside from the extra cash, Levitt says it also keeps boredom at bay.

A rising share of Americans is holding jobs into their golden years, bucking the overall trend of people leaving the labor force that is concerning Federal Reserve policy makers trying to boost growth. As the elderly continue to work, their paychecks are fueling spending and contributing to the U.S. economic expansion.