"I've always been an athlete,” Dr. Frederic Silverblatt, who is 80 years old, told NBC 10 News. “I was captain of my swimming team in high school and college in New York.”

That was well before Silverblatt became an infectious diseases specialist and the director of South County Hospital's Lyme Disease Clinic.

But he said he didn’t even start running marathons until he was an adult.

"I did the Boston three times," he said.