So what has kept them young?

"Staying busy. And good genes," says Gwen.

"Just working. And my wife," added Art.

It turns out, there is scientific data to back up their claims.

"We have known for a long time that people in the workforce are better than people out of work," says Laura Carstensen, founding director of the Stanford University Center on Longevity, addressing a forum on aging at the National Academy of Medicine last month in Washington.

"Work - paid or unpaid - may improve cognitive functioning."

Regular exercise and a Mediterranean diet are also known to help foster healthy aging.

"Geriatricians I know say that if we could put exercise in a pill form it would be the most sought-after drug on the market," she says.