Waste of time, waste of mind.
College professors last longer intellectually because their brains are always in motion. From having to deal with bizarre questions from students, to being forced to public certain amounts of academic papers, the lives of professors widely differ from those of 9-5 workers.
And thus, I have created this graph to show the waste of time and waste of mind created by inaction on part of the individual. Ability to learn decreases with age because of the distance away from an educational environment. With less new information going in, less information has to be processed -- and thus the capability to absorb new ideas and methods atrophies and is difficult to restart again.