Rich famous young superstars grow up? On planet Earth? Since when?I didn't know it, but according to Wikipedia, Lennon was already married to Cynthia Lennon and had a child, Julian. If that's the case, you grow up, you don't move on.
Maybe once they loose some of that (youth, wealth, fame). Unfortunately, Lennon lost all of that when someone walked up to him on the street and shot him. Lost his chance to grow up as well.