I'm reminded of this story from a webpage on San Francisco running "superstars". While I think genetics is a significant factor in determining your base energy

I'm reminded of this story from a webpage on San Francisco running "superstars". While I think genetics is a significant factor in determining your base energy level and how far you go, I think most of us have a lot more potential to regain lost energy than we realize: "Sister Marion Irvine did not start running until age 47. She was overweight and smoked two packs a day. Looking for a way to relax after a day as a grade school principal in San Rafael, Sister Marion took up running. ''I needed to use up some pent-up energy, so I decided to give it a go,'' said the 54-year-old Roman Catholic nun, who was soon going 70 miles a week. She started out half-running and half-walking. In 1984, she qualified for the US Olympic Trials in the marathon by running 2:51 at the age of 54, becoming the oldest to ever qualify for the OTs."