"First, let's look at how to define young adult fiction. The target demographic is 13- to 18-year-olds, sure. But authors and publishers are aware that adults read these books, too. Really, there are two pillars that define a YA book. The first pillar is that the protagonist or protagonists have to be in the aforementioned age range. The second pillar is the presence of the bildungsroman or coming-of-age story.
That's it. There's no requirement for whiny teenagers or angsty relationships. While some of their problems are very teenage and seem insignificant to adults, others are very real-world, grown-up problems being faced by people too young or experienced to have to tools to deal with them. Wars happen. Friends and family members die. Monsters attack. If conflict can arise in an adult novel, it can certainly rear its head in a young adult novel."
