Sixty-five. It used to be the magic number signaling time to slow down, quit work, buy that winter home in Florida, spend more time with the grandkids.

Not anymore.

With life expectancy in the United States at a record-high 77.9 years, experts in the field of aging are urging baby boomers to look ahead to a post-retirement career in much the same way they plan financial investments. To paraphrase a popular saying, 65 is the new 55. And there's virtually no reason for people to stop working just because they hit an arbitrary number.

"Retirement age is increasingly an historical artifact rather than a reality," says Joseph F. Coughlin, director of the Massachusetts Institute of Technology AgeLab, who has written and lectured extensively about the aging process and how technology can keep us healthier longer. "New careers, extending income, or simply staying active are incentives for many people to continue working and volunteering."

So is the chance to make a difference. That's what prompted Daniel H. FitzGibbon to take early retirement from his law practice and start a new career as a legal consultant to emerging democracies. "After 20-plus years, I decided there had to be more to life than what I was doing," says FitzGibbon, who travels the globe evaluating and recommending reform of judicial systems.

FitzGibbon discovered his passion in 1998 during a one-year sabbatical of sorts. He spent that year in Russia as part of the American Bar Association Central European and Eurasian Law Initiative and conducted workshops and seminars on commercial law topics. The experience was transformative. "When I came back, I tried to get back into the practice, but it really wasn't inspiring."

FitzGibbon had changed careers once before. After graduating from the U.S. Military Academy at West Point in 1964, he envisioned a life in the Army infantry. During the Vietnam War, he served as a captain with the Fifth Special Forces Group (an experience that he later turned into a book, To Bear Any Burden: A Hoosier Green Beret's Letters from Vietnam). With the war over, his interests shifted and he enrolled at Harvard Law School.

His years at the firm were lucrative, which made this third career possible. In most cases, he is paid for his international work, but the amount is nominal. "Money has always been secondary to me," he says. His philosophy has been: Find work that is interesting and important, and the money will follow.

FitzGibbon describes himself as semi-retired. He remains "of counsel" to the Indianapolis law firm Barnes & Thornburg just to keep his foot in the door. His overseas assignments come in intense spurts. He's been to Azerbaijan, Serbia, Bulgaria, and Kosovo, to name just a few. At 65, he sees no reason to stop what he's doing. Why should he?

According to the Encyclopedia of Aging & the Elderly, 65—the almost universal retirement age—has no legitimate public policy basis. Otto von Bismark of Germany picked the number when he launched a social security system for German workers in the late 19th century. "Somewhat cynically, Bismark knew that the program would cost little because the average German worker never reached 65, and many of those who did lived only a few years beyond that age," the encyclopedia explains. By the time President Franklin D. Roosevelt signed the Social Security Act of 1935 into law in this country, life expectancy was just under 62 years.

Today, 62 is the youngest age at which Americans can begin receiving Social Security benefits. Yet most people will live many years beyond that. As of 2005, the latest year for which figures are available, life expectancy for women was 80.4 years; for men it was 75.2. As a practical matter, people need to think twice before retiring. That's because, for most Americans, Social Security will be their number-one source of income.

Ironically, employers themselves are now leading the charge for older workers. Although age discrimination remains a leading complaint category at the Equal Employment Opportunity Commission, the numbers of complaints have been dropping since 2002. With the first wave of baby boomers eligible for early retirement plans, businesses are realizing they need older workers to survive. Certain industries, including aerospace, health-care and utilities, face severe labor shortages. It's a demographic "perfect storm." The decline in U.S. births after the baby boom is coinciding with the aging of boomers themselves. Barring an increase in immigration, there will be five million fewer workers ages 30 to 44 in 2010 than there are today.

Statistics such as these have fueled a whole new look at the job-training sector, which has previously focused its attention on younger and dislocated workers, typically manufacturing employees who have lost jobs during downsizing of their industries.

In August, Civic Ventures, a think tank based in San Francisco, teamed up with MetLife Foundation to encourage community colleges to offer services to "those in the second half of life." The partnership will award 10 grants of $25,000 each to community colleges that develop innovative ways to prepare boomers for second careers in healthcare and social services.

"We know that most Americans will need to work in the time of life that used to be called ‘retirement.' But how will they hone their skills and find opportunities that match their desire to work for the greater good?" asked Marc Freedman, founder and CEO of Civic Ventures (whose mission statement is, "Helping society achieve the greatest return on experience").

"Community colleges can provide a critical service, preparing boomers for work they want in the nonprofit, service sectors that need them," Freedman said.

Services are popping up to hook up older folks and jobs. On retiredbrains.com, people can distribute their resumes to companies in their part of the country and employers can search for workers by industry, experience level, and salary range. The website also links to charitable organizations and nonprofits looking for volunteers.

A similar service is available at retirementjobs.com, which offers online classes as well as advice with resumes and job interviews, salary negotiations, and tips on starting your own business. It also posts inspiring stories of baby boomers who have changed directions at midlife, becoming everything from professional chefs to dog trainers.

Even the government wants to keep older folks in the workforce. In times past, the rules of Social Security dissuaded people from working once they became eligible for benefits.

Legislation passed in 2000 eliminated the earnings limits for anyone who has reached Social Security's full retirement age, which ranges from 65 to 67.

Continued employment is generally good for the pocketbook, especially if employers offer health insurance and 401(k) plans. The only downsides: Some workers may not be able to access pensions from prior employment because they're not fully retired; also, working after retirement could place some people in higher tax brackets.

While money is important, it's hardly the only reason for older people to stay employed. In 2003, the AARP conducted a "Working in Retirement Study" to evaluate the desires and needs of an aging workforce. As part of the study, the AARP surveyed 2,001 people between the ages of 50 and 70 who were employed full or part-time. Of that group, 85 percent had not retired; 15 percent had retired from a job and either returned to the workforce after a short break or moved into a different line of work.

The surprising consensus: Seventy percent of workers who had not yet retired said they planned to work past 65 or never retire; almost half said they'd like to work into their 70s or beyond. Only 29 percent said they did not envision working for pay in any capacity.

Asked to select the primary factor behind their desire to keep working, 22 percent said money; 17 percent said health benefits, 15 percent said they want to stay mentally active and 14 percent said they wish to remain productive or useful. Other reasons include helping people, doing something fun, learning new things, or pursuing a dream.

Many of those reasons attract older adults by the hundreds to a program called Experience Corps, which matches them up with public-school children for one-on-one and small-group tutoring. The program began in 1995 in New York; Philadelphia; Minneapolis; Portland, Oregon; and Port Arthur, Texas. It has since expanded to 19 cities.

Tutors receive intensive training in childhood literacy, reading strategies and childhood development. Plus, they receive stipends funded in part by the schools and other private and public sources. The program has been cited as a model, not only because of its intergenerational approach but because it's producing results: Student reading skills tend to go up a whole grade level.

Businessman E. H. Klink was pursuing a dream when he signed up for an art class in his late 40s. "I just started asking myself questions. Why was I working as hard as I was?"

A West Point and Harvard Business School grad, Klink decided he didn't have to keep up the frenetic pace of the business world. He had enjoyed an extremely successful career acquiring growing companies and had the luxury of starting anew, minus the pressure to make money. Now 64, he's a full-time artist in Santa Fe, New Mexico. His distinctive landscapes can be found in the finest galleries starting at $1,000 (for more information, e-mail: ehklinkart@aol.com). And he can't imagine retiring. "You can paint forever," he says.

This much is certain: Post-retirement careers will be as varied and individualized as the hues in Klink's paintings. Some people, for financial reasons, will opt to continue in full-time positions; others will work full-time as volunteers. Yet others will use "retirement" as a chance to finally become their own bosses. The U.S. Department of Labor reports that boomers (those born between 1946 and '64) and older entrepreneurs account for 54 percent of self-employed workers, up from 48.5 percent in 2000.

"One of the greatest human achievements of the last hundred years is adding 30 to 40 years to our lifespan," says MIT's Coughlin. "But here's the problem. Now that advances in medical science, engineering, nutrition, sanitation, and physical fitness have extended our lives, we as a society have not even begun to think about how those extra decades will be lived."

FitzGibbon isn't like most baby boomers. He's given it a great deal of thought since having open-heart surgery at age 38. It sounds cliché, but that medical emergency convinced him that every moment is precious, that our time on earth is limited, and that one shouldn't put things off. These days he takes physical fitness seriously. He has run 10 mini-marathons and the Chicago Marathon in 1996. His heart is far from perfect, but he's doing what he can to age well so he can keep making a difference in the world.

Because FitzGibbon has been so enthusiastic about his retirement job, he often gets questions from people considering the same. And he's developed some stock advice. 1. "Make sure you know what you're getting into. If you can, try it first like I did in Russia. 2. Save money. In most cases there will be a reduction in income. 3. Don't burn any bridges with former employers. And maintain any professional licenses you have."

Plan ahead, just like you would for any major life change. As FitzGibbon has discovered, a retirement career can be the most fulfilling time of one's life.