In the economic downturn that began in late 2007 and persisted through the middle of 2009, millions of people in their 50s and 60s were laid off, bought out, downsized or otherwise left without a steady paycheck. The Center for Retirement Research at Boston College, in a report titled, “How Will Older Workers Who Lose Their Jobs During the Great Recession Fare in the Long Run?” found that the recession hit many more workers over 50 compared with previous downturns.

By 2012, many of these people were still out of work, said Matthew S. Rutledge, a labor economist at the Center for Retirement Research and a co-author of the paper. “It was really difficult for them to get back in,” he said. “It didn’t matter if they had retired or were laid off.”

The stock market decline and the collapse of the housing market also took a huge toll on the financial resources of older Americans. For those without jobs, that put even more pressure on them to return to the work force and impelled many to keep working well past their original target for retirement.

One result is that the work force is growing older. According to Andrew G. Biggs, an American Enterprise Institute resident scholar and a former top official at the Social Security Administration, there are 3.9 million more workers ages 60 to 64 today than in 2005, the last full year before the beginning of the economic slowdown. By comparison, he noted in an op-ed in The Wall Street Journal, there are fewer Americans ages 20 to 55 working today than in 2005.

For older Americans, paths to returning to full-time work vary. Some go into consulting, others seek specialized knowledge and new contacts by working as a volunteer. Still others resume their education through courses online or at a for-profit or community college, while some enroll in professional association courses. Many decide to start a business.

The biggest challenge for those seeking a new job after an extended period of unemployment is updating their skills for the current workplace.

“If you have been laid off or retired for a couple of years, skill sets may have moved on quite rapidly without you,” said Mark Schmit, executive director of the SHRM Foundation, a research affiliate of the Society for Human Resource Management. “This puts you at a disadvantage to the people who are working, including peers who are the same age.”