I'm even going to give you two more sources to look at. So please, give me an article that says rb's do not age faster than other positions, carries do not affect career outputs, and there's a drop off in productivity at a certain age. http://www.footballperspective.com/a-closer-look-at-running-back-aging-patterns-part-ii/ https://www.profootballfocus.com/blog/2012/07/16/age-of-decline-rb1/