I know a guy who ran 20+ miles a day, cycled stupid amounts etc.. and looked as fit as a fiddle. He had the kids one day and wasn't feeling too well for a couple of days, so he went to the doctors for an appointment. The doctor checked him over and said, "Any chance you could get someone to pick your kids up". "Yes certainly, why". Doctor said, "You need to go to hospital, an ambulance is on the way because you had a heart attack". So that's the end of of his fitness regime, he's been told by the doctors that anymore exercise could kill him. He's in his 30's.
The heart is like a stopwatch until it finally stops. It depends how fast you want to run it to the end. So I did all my cycling and running days and quit over 10 years ago, I'm in my 50's now.
Some guys are fortunate like yourself, some are not.