Okay, I thought that you were thinking that the problematic themes needed to be there I misunderstood your intent with the first comment. To answer your second question, take Japan for example, manga is ver popular there which almost all are told about teenagers. When citizens of Japan and writers of Manga were talked to about why they said they like to have young protagonists to relive their childhood days or to feel young again while reading even if it is fantasy they relate to the characters and their young problems.