“I said, ‘I don’t have medical experience,’ ” Ms. Delaney, now 66, recalled. “They said, ‘You just need to have common sense.’ ” A week later she went in for an interview. Today, she works four hours a day, five days a week, at Boylston Place, an assisted-living facility in Brookline, Mass.

“It’s quite a switch,” she said.

Ms. Delaney’s story is an object lesson for retirees. Many worry that their existing skills aren’t applicable to new industries, that their expertise isn’t transferable and that they will have to reinvent themselves to remain competitive. This, of course, can be overwhelming.

“There’s a real myth around reinvention, particularly when you talk about people in their 60s and 70s,” said Nancy Collamer of Old Greenwich, Conn., a semiretirement career expert and author of “Second-Act Careers.” “Why would you want to throw away all of that life and work and professional experience? It’s so much more about reconfiguring, taking the old and blending it with the new and coming up with something that’s going to excite you in the second half of the third quarter.”

A 2008 AARP study found that 83 percent of workers were interested in programs to build new skills and advance their careers. Ninety percent, however, wanted training to update their current skills and knowledge.

“It’s so much easier for people to do that if they can lean upon some aspect of what they did before,” Ms. Collamer said. “It doesn’t mean if you’ve been an accountant in a corporate setting that you find another accounting job. The goal is to take a step back and look — ‘O.K., what is it about being an accountant that I really enjoyed?’ You might discover that the thing you enjoyed most was going to the conference and meeting other people in the field.”