60, I do light cardio 3-4 times a week. Years ago when I ran 30-35 miles a week, my resting pulse rate was 36... A pulse can be too low. In the Air Force, a pilot's RPR needs to be above a certain number (not sure what it is). When pulling high G's, too low of a pulse can cause you to pass out. When mine was 36, I was lying down on a couch for an extended period, I stood up too quick, and I almost blacked out!
The blues had a baby, and they named it Rock and Roll