Larry Minnix, president of LeadingAge, an association of nonprofits that serve the elderly, said many older Americans were eager to continue working, but perhaps not at the same stressful pace.

“There comes a time when you’re not going to continue hitting cleanup for the New York Yankees, but they’ll keep you in their coaching system,” he said. “Older workers might not want to work full time, and many companies are being flexible with them. These workers often play a mentoring role, a leavening role in the organization. They contribute toward a healthy culture in the organization.”

Some experts on aging say the baby boom generation has changed the definition of retirement. “There’s a joke going around,” said Ms. Banda of AARP, “that the new word for retirement is ‘work.’ People are living longer and healthier lives — they want to stay active and engaged. For a lot of boomers, their definition of retirement is cutting down to part time or doing something on a project basis.”

Douglas Brown, 62, worked for 33 years doing marketing for Michelin, typically getting to work at 7 a.m. and heading home at 6 p.m., helping the company sell high-performance tires for Porsches, Mercedes-Benzes and other high-performance vehicles. He formally retired from his full-time job in January 2013, but as part of an arrangement to allow workers to scale back their hours and the demands on them, he resumed work at Michelin three months later.

Now Mr. Brown works two days a week at his longtime workplace, the company’s American headquarters in Greenville, S.C., mentoring and advising younger marketing employees, giving them tips on analytics and brand building to help them improve their performance. Exploiting the strong ties he has developed with dealers, he recently spoke to a group of Porsche dealers about the advantages of tires that Michelin developed for the new Porsche 918, a hybrid gasoline-electric vehicle.

“I never really wanted to retire, to go home and sit in a rocking chair,” Mr. Brown said. “I wanted to slow down. I wanted to do something that was applicable for my background and experience.”

Unlike many older Americans, Mr. Brown said he did not need to continue working for the money. “Growing up with Depression-era parents, you learn to save very well,” he said. He said he liked working part time because he appreciated the “social aspects of work life” and because he still had a passion for the automotive business. Michelin recently sent him to an auto race in California to give a behind-the-scenes tour to a group of auto industry insiders and bloggers.