Books are a category of entertainment that are all over the place. With so many authors out there, genres and sub genres are gonna have similar ideas fleshed out differently. Just like with movies, hard to have an original idea without borrowing some stuff. The major difference is, movies have trailers. Books have a blurb on the inside flap. Grabbing a random book off a shelf can be an intimidating thing. Will the author write in a friendly manner? Will it sound casual or formal? Is it a series, or stand alone? Hyper detailed or simple definitions?

Didn’t like your book? Go get a recommendation from a different source. Clearly you have a tone you are looking for. Some people like Tolkiens Silmarillion, and some people like Twilight. Both are fantasy, and they are drastically different.

YA stands for young adult. An adult is someone(in most of the US) 18 and older. A young adult by logical extension is probably in their 20s.