I wasn't 100%, so I did some research:
According to a few resources (none of them I'm betting my life on), YA (Young Adult) books are targeted at the 14-21 age range. /resource info
YA themes tend to or do revolve around younger protags with younger voice. What's appropriate subject matter is open for debate. Am I right (or crazy)?
But let me lay this at your door:
My local library shelved A Game of Thrones... in the YA section.
For those of you who haven't read George R. R. Martin's rather thick tome o' fantasy: It deals with some POV characters that are younger, but the book includes (a far amount of) sex, rape, language (F, S, C... you get the picture), and some semi-gross battle scenes.
I personally loved the book, but I don't know what I think of it being in the YA section. Granted, most of the teens at 14 have heard (or at least THINK they have heard) it all. Then there's sheltered children, like I was.
What are your thoughts? Does it matter? What of Lord of the Rings? Should that be YA?
I talked to a librarian in Tech services. She says that YA is 17-25 or 30 (I can't remember exactly what she said.) Below that is Junior Fiction(?). Huh.