So it seems the reading age-range for YA is 13-14 years old. Always a little younger, because teens 15-18 are heading for the adult books by that time. Although I'm sure there are exceptions, with some older teens reading young adult novels. (The same as there are exceptions with adults who read YA novels.) It's really a little too bad that they are separate, because some adults and teens are missing out on good YA stories.
One point that I've read recently is that even with a good plot or unique storyline, the novel still has to be character-driven. Not simply one quest after another until the end. The character has to have motivations, true feelings, struggles, and they have to change during the course of the book (what have they learned?). Some of my stories do that more than others, I have to admit.