already too big for his britches?

Me:  How did you get to be such a smartypants?  Where did you get those smartypants?

Simon:  I don't know.

Me: Did you get them from me?

Everett: No, he gets them from me after I get too big for them.

I was wondering how that aging thing went down

Everett:  Teenager is when you are in the teens and after the teens you are a very old person and then you always stay a very old person - oh, I mean, grown up.