Imagine: Nothing has happened in months and you and the pack are bored, so you all make it your mission to get Peter to admit his age. You each contribute $5, and the person who guessed the closest number to his real age gets it all after you find out. (You would think Derek would know, but Peter’s just that shady.)
Imagine being Scott’s younger sibling and that when Derek is returned to his younger self, he is stuck like that and you start dating him secretly. Obviously, Derek doesn’t know why Scott might object, and doesn’t know why you don’t want him to find out.