Of the right age, but can't seem to stay retired

Suzy Boerboom, a registered nurse, retired - for the first time - after a 35-year career in healthcare and ownership of several Curves exercise franchises. She then devoted five years helping her three daughters raise their children.

"I was very close to both my grandmothers," Boerboom said, "and I wanted the same relationship with my grandchildren." But after several years, she felt too restless to retire, she said. "I just didn't feel relevant," Boerboom, now 66, said. "I was beginning to feel a little bored and a bit out of the mainstream."

So in 2009, she started Welcyon, Fitness After 50, a health club business that aims to help older people become fit and stay that way. Boerboom, working with her husband, Tom, from their Edina, Minnesota, headquarters, is now busy franchising the centers.

Boerboom said she "failed" at retirement, joining a group of people who sometimes are labeled workaholics or, more kindly, "driven achievers", who work simply because they love it. For many, the "ideal retirement includes work in some capacity", says Ken Dychtwald, founder and chief executive of Age Wave, a group that researches the aging population.

Many retirement dropouts are highfliers who land right back in the executive mix. Of course, many over 55 work to pay the bills, but others just want to keep busy, so they help a family member's business.

These workers are swelling the ranks of the workforce ages 55 years and older. There are more people in the retirement-age workforce than at any time since the 1960s, the federal Bureau of Labor Statistics has found. About 33 million seniors are employed, up 49 percent from the 23 million such workers a decade ago, according to the government data.

This is a reversal from the 1950s when, benefiting from Social Security and company pensions, people began retiring at earlier ages than ever before. In 1960, according to federal statistics, only about 40 percent of workers over 55 were in the labor force compared with nearly twice as many, or 80 percent, in 1900, an era when relatively few people ever left work unless they had to because of illness or physical disability.

By the 1970s, the percentage of the upper-age labor force fell even further, to the 30 percent range. But it began climbing back up again in the late 2000s, spurred by the economic collapse in 2008. This year, the 55-and-older segment returned to 1960s levels of around 40 percent, as many people work to rebuild their retirement savings or supplement their Social Security payments.