It's not my rules. It's what we know giving the information that Marvel has provided. It wouldn't make sense to cast a 23 years old to play a 15 years old Peter Parker, just like it wouldn't make sense to cast Dylan O'Brien to play a 15 years old Stiles NOW. Can you understand that? Dylan would be right and a strong contender four years ago. I feel like a 19-20 years old actor (not all of them, but some) can play convincing 15 year olds, just like O'Brien did with Stiles all these years. The thing is, Marvel is casting for a 15-16 teenager now, and O'Brien was cast as a 15 year old Stiles four years ago. He doesn't fit that age anymore, it's just that, the age limit is real, and it should, so Marvel can choose an actor that we all can believe is a 15 year old.