hmm.. i would say when he's standing up from gettin back from his break and you're a foot taller than him.
pshhh.. your never too old for santa clause! :P
but I would say - When you're about ten years older than all the other kids lined up to sit on his knee :)
Exactly. When you walk by and are like, "He's probably a pedophile. I bet there's a molester mustache under that fake beard".