DETROIT — When May Jackson was a young girl, there weren't many chances for her to play volleyball.

So now at 78, Jackson can be found at least once a week on the wood floor at the Older Persons' Commission center in Rochester, Mich., bumping, setting and spiking balls, along with her teammates on the center's 70 and older volleyball team.

For Jackson and her husband, Glen, also a volleyball player, the sport is imbedded in their lives. They travel a few times a year to places like Utah and Texas to compete in senior tournaments.

Across the country, older Americans are redefining aging. Gone are the days when shuffleboard, knitting and bingo were the main activities for older people.

Now they're likely to participate in team sports like basketball, volleyball and softball. Or to run marathons.

Events like the National Senior Olympics to be held next year in Louisville, Ky., are expected to draw about 12,000 senior athletes from across the country.

At the Michigan Senior Olympics this month, athletes competed in team sports, as well as tennis, golf, badminton, canoe and kayak racing, track and field events, road racing, cycling, swimming and archery.

More metro Detroit seniors competed in events like the Downriver Senior Olympics in August, and the Western Wayne Senior Olympics, in Northville in September.

In August, Jackson and her teammates from the Older Persons' Commission went to Kalamazoo to compete in the Michigan Senior Olympics; the annual event drew about 1,000 senior athletes.

"You know how you used to bring your children to all their sport games?" May Jackson asked. "Now there are young people who come and bring their parents. It's really great."

"As we get older, we are still young," said Monty Cartwright, an associate professor in health and physical education at Southern Oregon University. He is conducting a study on athletics and aging. "There are consequences, of course, on the body. Most senior athletes can do everything they used to do, just not as fast or as high."

Cartwright, 62, decided that his birthday gift to himself would be to run the San Francisco marathon July 30. His 57-year-old wife ran with him.

Seniors are also living more actively.

Lincoln Park resident Jay Thompson, 77, has been playing softball on senior teams since 1993, six years after he retired from his job as a GM engineer. He also travels a few times a year to participate in tournaments across the country.

"If I quit softball, my wife would be upset," Thompson said. "She says it keeps me alive."

Thompson's team, Half Time Bar Taylor, plays twice a week. The men, for the most part, are fit, tanned and fiercely competitive.

"They're out here for the game, for the competitiveness," said Forrest Saylor, 81, who manages the team. "Nobody's out here just for the exercise. That just comes along with it."

For many of the men, a passion for baseball began when they were young. And true passion doesn't die over time, even though they did have to make the shift from baseball to softball.

And forget about night games. They play at 10 a.m. twice a week.

"I been playing forever," said 73-year-old Neil Jackson, who plays for a Half Time Bar team. "It's still more fun than playing golf."

Many of the men say they'll play until they can't any longer.

"I always tell people, 'Consider yourself lucky at our age, we're able to get out here,"' Saylor said.

That older Americans continue to be involved in athletics can be credited partly to societal changes, said Cartwright. His study is based on responses to a survey on his Web site, www.sou.edu/PE/survey, that asks athletes questions about their active lifestyles.

"A few generations removed from where we are today, people didn't have discretionary leisure," Cartwright said. "People didn't get to retire."

There are also more opportunities for staying active, which wasn't the case a generation ago.

"When my dad retired, he went right to the sofa," said Mort Friedman, 70, who plays with Thompson on the Half Time Bar Taylor softball team. "He didn't have anything to do."

Now older adults can play golf, tennis or team sports like softball and volleyball, go to exercise classes, train as runners or cyclists and compete in tournaments.

There's a caveat, though. While some older Americans are staying involved in athletics, many others still don't get the daily amount of recommended exercise they need, said Margaret Hawkins, manager of health promotions at AARP in Washington, D.C.

"We know people know the benefits. They really know they should" exercise," said Hawkins. "It's the doing of it and the time — they feel they don't have the time. Those that are active make the time."