I heard somewhere that when a group of kindergarteners is asked "who in this room sings?" that the entire class will raise their hand, but just a few years later when the same group of children is asked the same question very few raise their hand. Just recently I heard something similar, but the question was "who is the smartest person in the class?". The younger group all responded "I am" while the older group all called out a different kid in the class.
I think that the same thing applies to running. We all ran when we were younger. Somehow at some point in our lives we just stopped. Why? Just like the chef in the movie Ratatouille says "anyone can cook", I believe that anyone can run. We did it when we were kids. We can do it again. All it takes is the decision to start.