Anecdata: I ran marathons and a few ultras (several 36 mile, one 50) in my late 20s. Through my 40s and 50s, my EKGs, and one ultrasound of the heart, have all come back clean; I'm not sure whether I've had one since turning 60. I'm 63 now, and haven't run for a couple of months, but that has to do with plantar fasciitis that I let get out of hand.

The craziest of my running friends, measuring by ultras run, has said that she doesn't run far these days, but that's her knees.