Another reward of working out is eating more.

"Even though your basal metabolism slows down as you age, you can make up some of that as you exercise," said AARP features editor Gabrielle Redford. "Your systems are slowing down, but you can challenge them and take years off your real age. If you're 50, get the body of a 45-year-old by exercising."

Osteoporosis can also sneak in during your 50s and 60s, so be sure to add exercise that is weight-bearing, whether that be walking, jogging or lifting weights.

"Classes popular with our seniors are in water, but you can't build bone density in water," Rick said. "You can get joint and bone benefits from 20 minutes twice a week with a ground workout."

During this type of exercise, your skeleton adapts to the pressure of gravity by building more bones, Shape Magazine reported.

No matter what you do to stay active, support that commitment with diet.

"I've seen my peers grow old and end up carrying as much weight as another human being on their back. I eat everything in moderation," he said.

Harris said combining the two has kept him within 5 pounds of his graduation weight.

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