Thanks for your question! None of the age cutoffs in the game are very strict aside from the drinking age (14) and the age of majority for participation in adult content/legal drug use (18). As far as the cutoff for the Perimeter Guard, you can play it however would be most enjoyable for you - if you'd like her to have to fight for her right to be with the adults, go for it; if you'd like her to get straight in with no fuss, that's fine too!