Too young looking persons on the screen

So, I can't upload a cum tribute for Maisie Williams because she "looks too young"? Of course I have chosen a picture where she is already 18 years old.

Yes, I read the the FAQ. It says

We remove videos and photos that violate our terms. Never upload:
- Videos/photos involving u******ed persons, also videos/photos with persons looking young (even if they are 18+ but look like they are younger)

Who decides which person looks younger? And why is Selena Gomez ok then?