Even at age 70, Ron Hustwit has no itch to retire.

He has taught philosophy full time at the College of Wooster, Ohio, for 46 years and, unlike friends and colleagues who chose to retire long ago, he still enjoys going to work.

“I don’t have any days when I say I have to put in another day at the office,” he said.

Hustwit is one of a growing number of seniors who are opting to remain in the workforce.

The U.S. Census Bureau reported that the percentage of people 65 or older still working rose from 12.1 percent in 1990 to 16.1 percent in 2010, driven largely by women. And its latest survey report shows an even higher number, 19 percent.

The reasons are varied. Some seniors are doing it strictly for the money, knowing they don’t have enough saved to retire or worrying that they’ll outlive their savings.

Others like Hustwit know they would miss the social interaction at work or they have no desire to take up a hobby such as golf or traveling.

Then there’s a less obvious reason: Service and office jobs don’t require major physical labor, allowing seniors to work longer or even enter the workforce later in life.

“People are living longer, and they are healthier,” said Paul Magnus of Mature Services, an Akron nonprofit that helps older workers find jobs. “To look at age 65 and think you have two decades left of active lifestyle, work is part of it.”

Retiring at a younger age is a relatively new concept, he said. Before, most people worked until they died.

Harvey Sterns is director at the Institute for Life-Span Development and Gerontology at the University of Akron and author of the book “Working Longer.” Sterns, 70, still works full time and grew up in a family that owned a store. “We used to say in the Sterns family: ‘You die in the aisle making the sale. But you first finish the sale,’ ” he said.

While the trend of more seniors working is likely to continue, Sterns noted that others have no intention of working longer than they have to.

“We have to remember that a lot of people don’t like their work,” he said. “Work is only there to get money to do the things you really want to do.”

During a jobs program at Mature Services, people (not all were over 65) were asked why they wanted to return to the workforce.

The No. 1 answer involved money.

Some said they or their friends didn’t plan well enough for retirement. Or, because of the recession, they started raising their grandchildren and needed the income.

Another popular reason was social. They don’t want to sit at home alone.

Sterns said women often enjoy the social interaction at work more than men, or they are forced to re-enter the workforce after a divorce or raising a family.

Hustwit fears he would miss the intellectual stimulation, friendships and reason to get out of the house each day. He also has no plan for what to do next. “My picture of retirement is really just sitting around and wondering what I’m going to do,” he said.