The study by the Pew Research Center, an independent research group, highlights a rapidly graying labor market due to longer life spans, an aging baby boomer population and a souring economy that has made it harder to retire.
Pew's survey and analysis of government data, being released Thursday, found the share of Americans ages 55 and older who have or were seeking a job rose to 40 percent this year, the highest level since 1961. In contrast, people 16 to 24 who were active in the labor market decreased to 57 percent, down from 66 percent in 2000.
Asked to identify why they're working, 54 percent of older workers responded that it was mostly because they wanted to, citing a desire while they were still feeling healthy to be productive, interact with other people or to "give myself something to do." A sizable number of them - nearly 4 in 10 - also acknowledged staying put at work partly because of the recession.
Among young people 16 to 24, nearly half the respondents said they weren't working because they wanted to focus on school or job training, reflecting a growing view among Americans that a college education is needed to get ahead in life. About 4 in 10 said they looked for work but couldn't find a job.
In all, the number of older workers is projected to increase by 11.9 million in the next few years. They will make up nearly 1 in 4 workers by 2016.
"When it comes to work, this recession is having a differential impact by age. It's keeping older adults in the work force longer, and younger adults out of the work force longer," said Paul Taylor, director of the Pew Social and Demographic Trends Project. "Both of these trends pre-dated the current downturn, both have been intensified by it, and both are poised to outlast it."
Among other findings:
-The U.S. labor force is expected to increase by 12.8 million workers from 2006 to 2016, including the 11.9 million who will be ages 55 and older. Workers ages 25 to 54 will increase by 2.5 million, while those ages 16 to 24 will decrease by 1.5 million.
-After increasing for five decades, the share of women holding or seeking a job has flattened at 59 percent. That is about 13 percentage points below the rate of men in the labor market. Asked to identify their reasons for not working, women were nine times more likely than men to cite child care or other family responsibilities as a major factor.
-Older workers tend to be happier. About 54 percent of workers ages 65 and older said they were "completely satisfied" with their jobs, compared with 29 percent of workers ages 18 to 64. That reflected the fact that they were working primarily for more social reasons, rather than financial need.
-Most working mothers prefer a part-time job. Among those with a full-time job outside the home, 6 in 10 said they would like to have a job with fewer hours. By contrast, just 19 percent of fathers with a full-time job and a young child said they would prefer to work part-time.
"Public attitudes about women and work may have changed dramatically over the past generation, but mothers and fathers still experience the tug between work and family in very different ways," Taylor said. "Mothers who have children at home and work full time would rather be working part time, or not at all. Fathers who have children at home are glad to have a full-time job."
Pew based its findings on data from the Census Bureau and the Bureau of Labor Statistics. It also interviewed 1,815 people ages 16 and older by cell phone or landline from July 20 to Aug. 2 about their attitudes toward work. The poll has a margin of error of plus or minus 2.7 percentage points.