Publishers are always creating new categories ("Urban Fantasy" and "New Weird" for example), but YA (Young Adult) has been around for awhile. My teen years coincided with the heyday of S.E. Hinton, but even then I chafed at the idea of there being a separate category of books for teenagers and those for adults. I was reading mysteries and horror and sci fi but I was also reading history (my father was a Civil War buff) and popular science and "literature" for school.
These days, the YA category is probably the hottest thing out there, though, and keepng abreast of publishing trends means knowing what's going on in the YA category. Adventures in Children's Publishing is a great website for that. And they give away books. Who doesn't love free books? Check them out.