But financial need and the desire for new challenge are not the only factors driving how workers approach retirement. People are looking at decades, instead of years, of retirement, and they are rethinking traditional pastimes like travel, golf and bridge.

Further exploring motivation, an AARP survey, conducted in January, found that about a third of retirement-age people said they worked because they enjoyed it. That is equal to the percentage of those who said they had to work for financial reasons, according to the study called "Staying Ahead of the Curve: The AARP Work and Career Study".

The AARP research found that 55 percent of retirees are employed voluntarily, including the 25 percent who reported working because they wanted to be physically or mentally active.

The study queried 1,502 people 45 through 74. Such "driven achievers" include Ronald E. Stewart, chief executive of PRGX Global, a business analytics and information services provider, who segued from a 30-year career at what is now Accenture, beginning in the 1980s. He prepared for a postretirement life without a workplace, but also kept looking for business opportunities.

"I was the oldest guy in the Atlanta office," he said of his 2007 retirement at 53, and "I was tired of being constantly on the road for work." After winding down for a brief period, he decided to keep his hand in the working world by starting a private equity investment firm with former colleagues.

"It was a little bit of a toe in the water," he said of the venture. But then an unexpected opportunity enticed him to pursue a completely new business. In 2008, he opened a hamburger restaurant with a young man he had mentored for years while volunteering for Atlanta's "Big Brothers, Big Sisters" program.

Stewart quickly had to learn day-to-day restaurant operations after helping open FLIP Burger Boutique, which he calls "fine dining between two buns". "Waking up and doing something you want to do sort of gets in your DNA," he said. "I never felt comfortable chilling out, and I always had a desire to keep moving."

Part of that was serving on the PRGX board, and last year his fellow directors asked him to become chief executive of the 1,600-person company. Even though he is once again the "oldster" among his colleagues, Stewart said he had no plans to retire soon.

New York Times News Service