The useful man never leads the easy, sheltered, knockless, unshocked life

An interesting perspective on age and achievement by Thomas Edison in 1927 (when he was eighty years old).

The man who has reached the age of thirty-six has just about achieved readiness to discard the illusions built on the false theories for which wrong instruction and youthful ignorance previously have made him an easy mark. He is just beginning to get down to business. If he is really worth while he has passed through a series of hard knocks by that time. The useful man never leads the easy, sheltered, knockless, unshocked life. At thirty-six he ought to be prepared to deal with realities and after about that period in his life, until he is sixty, he should be able to handle them with a steadily increasing efficiency. Subsequently, if he has not injured his body by excess indulgence in any of the narcotics (and by this term I mean, here, liquor, tobacco, tea, and coffee), and if he has not eaten to excess, he very likely may continue to be achievingly efficient up to his eightieth birthday and in exceptional cases until ninety. Then the curve turns sharply down. The cycle is approaching the end. At about that age the entities which form that man will be preparing to discard their abode, which is that man, and enter upon a new cycle. Then and not till then men should, must and do begin to step aside.