Being grown-up

Hey, y'all,
This weekend was an exciting one for my grandson. He lost his first tooth Friday evening! He very seriously asked me if I knew what that meant. When I asked what, he replied "I am almost grown up!" And he meant it. He thinks that now that he has lost a baby tooth, and has "grown-up tools", and is in kindergarten, too, he must be almost grown up. I just told him not to hurry, because he will be a grown-up for a lot longer than he will be a boy. He wasn't impressed. Why do you spend 20 years wishing to be a grown-up, just to spend at least part of the next 60 wishing you were young again?
JB