Rhetorical Tropes:Paradox:..PLEASE EXPLAIN?

The young are too inexperienced, uneducated, uninformed, unskilled, etc., to realize the importance or enjoyment they get from being young. When one is old and wise enough to know how much fun it was being young, he is too old to do the things that young people take for granted - like running, playing, staying up all night, chasing girls (or boys), etc.