Until recently, working after retirement sounded like an oxymoron. Aren’t those years (stage of retirement age) supposed to be devoted to volunteering, traveling and visiting grandchildren? 

But a recent report by the Families and Work Institute and Boston College’s Sloan Center on Aging and Work found that a growing number of people continue to work for pay following their official “retirements.” And while they may be motivated by money, many like my father are finding their late-life jobs unexpectedly fulfilling.

Older workers “expect they have to, and they want to, extend their labor force participation,” said Marcie Pitt-Catsouphes, director of the center and the study’s co-author. In fact, 75 percent of the participants over age 50 in the center’s study said they expect to have jobs after they “retire.”

The federal Department of Labor estimates that between 2006 and 2016, the number of workers over age 55 will rise 36.5 percent. That increase will create the grayest labor force since the government began tracking this data, Mr. Johnson said.

Gray or not, my father strongly believes working keeps you healthy. “Any day I work, I feel good,” he said. He also believes the routine helps him sleep better.

My mother, scheduled to retire last January, told me she kept her hotel job to stay active and avoid boredom. But when I asked what she would do if she won the lottery, she said she would quit immediately: “I would just stay home and take care of the family.”

“Older workers describe it as a way of keeping young — that’s often the language they use,” said Ms. Pitt-Catsouphes. “They want to work because they enjoy the people they are working with or they want to be productive.”

Political developments may not make the situation easier for them. Recently President’s Obama’s bipartisan commission on reducing the national debt suggested gradually raising the Social Security retirement age to 69, a move that would transform many retirement workers into simply workers.

Still, my dad insists that even if he had a winning lottery ticket, he wouldn’t give up his retirement job: “I would still want to work, because I want to meet those people, all kinds of people.”