Childhood Logic

Mimi comes around the corner, pantless as usual, playing a game with her siblings.

Mimi: Na na na na na,, you can't catch me. ha ha haha ha, I the biggest!
Bear: No, you're not the biggest.
Mimi: Ha hahaha ha, I'n the boy!
Bear: You're not a boy, Mimi.
Mimi: no! I'n the boy! See my penis!?
Bear: you don't have a penis, Mimi. You're too little for a penis.

!!!!
How old are you when you grow your penis!!??

Um, Bear's a little confused apparently. Time for a biology lesson.