Dave Zarrow, who lives in Reston, Va., figures he spends about 20 hours a week in his 2017 Toyota Camry driving for Uber.

A former small-business owner who segued into teaching, he and his wife have left their full-time jobs and could comfortably retire. Even without the $15 to $20 an hour he earns driving, “we would have been OK,” he said.

But at 68, “I get antsy just sitting around,” he said. He likes the flexibility of this nontraditional job — no benefits and unpredictable income, but the ability to set his own hours — and his conversations with riders.

Besides, his earnings help pay for visits to far-flung children and grandchildren and other extras. “It’s allowed us to continue the same lifestyle we had before we retired,” he said, without eroding their savings.

He is not the kind of older worker in a nontraditional job that economists worry about.

They worry about people like Gary Ellenbogen, 64, who has spent three years driving for rival Lyft. Once a self-employed business coach and ski instructor, Ellenbogen worked in corporate sales for several years, then got laid off in his 50s.

He has struggled to find steadier work ever since. “Nobody’s interested in someone my age,” he said.

Despite spending 40 to 60 hours a week picking up riders in his 2015 Subaru Forester, Ellenbogen is barely surviving financially. He had to give up his apartment and move into his mother’s condo in Verona, N.J. He relies on Medicaid for health care.

“It’s something I’m accepting because I’m in need of money,” he said of his Lyft gig. “I’m capable of better things, but this is what’s available to me.”

Economists debate how to define this kind of employment, often categorized as “nontraditional jobs” or “alternative work arrangements,” and how to calculate the proportion of the older workforce engaged in it. Popularly seen as the province of the young, it provides work for a growing number of people in their 50s, 60s and beyond.

The federal Bureau of Labor Statistics includes independent contractors (who may be self-employed but well compensated) and estimates that 11.4% of those ages 50-62 have nontraditional jobs. The Government Accountability Office, using an even broader definition including part-timers, says the figure is 31.2%.

Among workers over 62, economists at the New School’s Retirement Equity Lab have found that 9% were in “on-call, temp, contract or gig jobs” in 2015; the researchers think the percentage has grown since then.

In an October report, the Center for Retirement Research at Boston College put the number of nontraditional job holders at about 20% of 50- to 62-year-old workers, using data from the national Health and Retirement Study.

Their study defines nontraditional jobs as those that provide no health insurance or retirement benefits. “They’re probably low-paid,” said Alicia Munnell, director of the center. “Some have erratic schedules.”

According to the report, only about a quarter of 50-year-old workers stayed at a traditional job with benefits until age 62; some classified as early retirees may not have left their jobs voluntarily.

The majority of those in nontraditional jobs at ages 50-62 rely on them for most of their employment, and their retirement income at 62 is 26% lower than that of employees holding traditional jobs. (Nontraditional jobholders have somewhat higher rates of depression as well.)

Economists generally approve of people extending their work lives, but in most of these cases, “the jobs they’re taking aren’t the kind anyone would take because they’re interesting,” said Teresa Ghilarducci, director of the New School’s Retirement Equity Lab.

Nontraditional jobs include food service and retail, as well as gig jobs; among the fastest-growing categories are janitorial work and personal care and health aide positions. “They’re not easy on older bodies,” Ghilarducci pointed out. “They require a lot of physical stamina.”

Their prevalence might help explain why so many workers claim Social Security before reaching their full retirement ages, reducing their benefits. When work becomes intermittent and poorly paid, the predictability of a fixed monthly check with cost-of-living increases can feel irresistible.

Some nontraditional workers ages 50-62 lack a high school diploma, but people with college degrees are also entering this sector. “They’re the ones that had a good job, then had a hiccup — the recession, a job that moved away — and had the most to lose,” Ghilarducci said.

Ellenbogen, for instance, has a master’s degree in social psychology from the University of Vermont. After getting laid off from sales positions and finding a return to business coaching unprofitable, he became a commission- only sales rep for the Home Depot, with no base salary or benefits.

The company let him go, he said, when retina surgery left him unable to drive for two months. After he recovered, the only work he could find was with Lyft, where about a quarter of drivers are over 50, the company reported last year.

Ellenbogen has searched for jobs on LinkedIn, on Indeed and in local newspapers. The New Start Career Network at Rutgers University has provided free weekly sessions with a coach.

Nothing has materialized, so Ellenbogen keeps driving, trying to delay claiming Social Security to maximize his benefits.

How to help support older workers whose precarious employment endangers their retirement? Several states have started individual retirement account programs, but with no mandated employer contribution, it’s not clear how much difference they’ll make. Broader national actions, including more affordable and accessible health care, would be more effective, Munnell said.

Even if Washington takes action to shore up retirement security, however, relief might not come in time for Ellenbogen.

He happened to be at a sales meeting in the Pentagon on Sept. 11, 2001, an experience that left him uninjured but persuaded that “you must find ways to smile and enjoy today.”

But that can be hard. This month a driver went through a stop sign and did almost $6,000 in damage to Ellenbogen’s car.

Though insurance will apparently cover the repair, his car has been in the shop for more than two weeks, temporarily leaving him with no way to earn a living.