This quote can be applied to anything and everything, especially running. Did you see the image going around of an 83 year old man who recently finished a 100k? Or the stories every marathon season about the 80, 90 even 100 year olds completing marathons? What about the amputees who have finished Badwater (arguably the toughest race in the world) ?
“Never too old, never too bad, never too late, never too sick to start from scratch once again.” – Bikram Choudhury.