When Carol Sue Johnson, 73, wheels her silver Mazda SUV out of her driveway in suburban Minneapolis, she doesn’t know how much money she will make driving for the ride-hailing service Uber, but she’s sure she will have an adventure.

Her passengers run the gamut, she said, from three visiting Chinese business executives who were surprised to see a female driver, to teenagers needing a ride to hockey practices or games.

When one group of teenagers “started to get too rowdy,” said Johnson, who goes by Sue, “one of them told the others to stop because ‘Grandma’s in the car.’ ”

Johnson is among a growing number of older Americans who are driving for Uber or its competitor Lyft to augment their retirement income. Some drivers say it is a great chance to be independent and earn extra cash on their own schedule. But others, including some drivers, say it is exploitation of older people who work as independent contractors, without any benefits, because their age means they have a harder time finding full-time employment.

Many retirees, like Johnson, drive part time, about 20 to 30 hours a week; others may drive full time, which in many ways takes them out of the fully retired category.

Drivers are in such demand that last July Uber and Life Reimagined, a subsidiary of AARP, the organization for people over 50, formed a partnership to recruit more people as drivers.

They are trying to tap into the 50-and-older workforce, a segment that is growing steadily, according to an AARP report released last year.

LIFE BENEFIT VS. JOB BENEFIT

As the population ages and more baby boomers challenge traditional retirement norms, the number of older workers should continue to rise. One reason is that many people are leaving the full-time work force with less money than they need to support themselves at a comfortable standard of living.

Uber, which surveyed drivers in 2014 and 2015, found that nearly one-fourth of its drivers were 50 or older.

Older drivers are prized because they usually own their own cars, have adequate auto insurance and, according to insurance statistics, have fewer crashes. Uber’s collaboration with Life Reimagined, a group that helps people navigate life transitions, provides access to the group’s 1.4 million members through online and in-person workshops. Through the alliance, Uber offers a $35 incentive for those who sign up to become drivers and drive 10 trips.

Molly Spaeth, a spokeswoman for Uber, said the company had enlisted nearly 600 drivers as of this month with its AARP collaboration.

Uber and Lyft — which said it did not track the ages of its drivers — and their supporters contend that on-demand employment lets companies provide work without the costly rights and perks like overtime pay and vacation time, that attach to full-time employees.

Besides, David Plouffe, an Uber board member, argued, most drivers work far less than full time. As many as half drive only 10 hours a week, he said in a speech in November, and 61 percent, or nearly two-thirds, have other job commitments.

But Uber does not break out the exact percentages of full-time and part-time drivers. Some drivers who work full time complain that in addition to not having benefits, they must work longer hours to earn a living wage, especially after Uber last year cut the rates it charges passengers.

FREEDOM AND FLEXIBILITY

Drivers in Seattle who belong to the App-Based Drivers Association, a group allied with the Teamsters union, won the right last month to negotiate pay and working conditions. That makes a lot of sense to full-time drivers like Musse Bahta, 42, who said he had to spend more time on the road since Uber lowered the per-mile fare to $1.35.

“You have to work close to 50 hours a week to survive,” he said, pointing out that he has to subtract payments for his new Toyota Camry, gas and maintenance from his gross income. “If I did Uber on the side, there would be no complaints.”

For most senior drivers, the biggest advantage is the extra income. Many of those who continue working after 65 do so because they would be too poor otherwise, according to a new report from the labor-backed Economic Policy Institute that found the current retirement system inadequate.

But driving for a ride-booking service, some retirees said, also can offer more than money.

“I love the freedom, the flexibility — and the cash coming in every week,” said Maureen Mahon, 59, who first saw an Uber advertisement on the side of a bus in Manhattan. Mahon, who lives in Brick Township, N.J., said she had been laid off twice in recent years from Wall Street, and has been driving intermittently since mid-2014.

“I meet businessmen, college kids on their way out for the night, folks going to parties, pretty much the whole range,” she said. “You can drive as much or as little as you like. If the weather’s bad or you have a doctor’s appointment, you just don’t turn on the app.”

Another attraction, compared to driving a taxi, is safety, since customers are screened and no cash is exchanged. Also, drivers can shape the job on their own terms.

Driving for Uber “is like a game,” said Stephen B. McPhail, 66, a former charter bus driver who lives in Covington, Wash., south of Seattle. “I like to map out how I spend my time to make the most money.”

An early riser, he gets up at 4:30 a.m. to land several airport rides. Typically, he said, “I work five hours to make between $100 and $150 a day, and I can be done as early as 10 a.m.” That leaves him plenty of time to be active in his church. “Sometimes I go ‘ubering’ after our Wednesday morning fellowship meeting,” McPhail said. He is trying to persuade his wife, Kathryn, to become a driver when she retires from her insurance-related job.

‘HELPS THAT GAS IS CHEAP’

In San Francisco, Dominic W. Angelo, 66, a retired solar industry salesman who drives for Lyft to supplement his Social Security income, works only on weekends. He leaves his home in Walnut Creek, about 30 miles east across the Bay Bridge, in time to arrive in the city by 8:30 a.m. on Saturdays and Sundays, where, he said, he picks up “a lot of people going to brunch, to the gym, to work and sometimes to the airport.” “I can make about $160 a day, driving until about 3 p.m., and head back over the bridge so I can be home in time for dinner,” he said. “You could make $50,000 a year doing this full time, but that would mean working Thursday, Friday and Saturday nights until the bars close.”

In Minneapolis, Johnson says most of her earnings come from ferrying executives between the airport and major companies, like Cargill and General Mills. At busy times, she can make around $40 an hour. Overall, she said, she works about 40 hours a month, grossing around $600.

As for keeping the car spiffy and the gas tank full, “it helps that gas is cheap these days,” she said. Expenses like repairs “have to be done anyway,” she said, “and you can write some of it off on taxes.”

“There’s no question that the money makes life easier,” said Johnson, who is divorced. “My kids think it’s a stitch that I’m doing this.”