If you have ever wondered what age is the "right" age to introduce kids to YA literature, read THIS post by Daisy Whitney.
I am the parent of a very advanced reader, and I have often struggled with what is and isn't appropriate for my daughter. She started Junie B. Jones at three, and was on to the Little House books by five. She read the entire Harry Potter series by the time she started 1st grade, and felt like she had read everything in the Juvenile section of the library (that was of any interest to her) by the beginning of 3rd grade. What do you do with a kid like that? If you are a good parent, you can't just point to the Teen/YA section and say, "Have at it!". You have to look at each book individually and decide if it is something that kid can handle based on not only reading ability, but maturity, life experience, and knowledge of the world around him/her.
My love for YA books started because of my daughter's alien-like reading ability. Even "Juvenile" books are typically written for kids between the ages of eight and twelve, so when she was six, I had to read them for content. More than once, I have nixed a book because it wasn't content-appropriate. (Some of those Newbery books should NOT be read by kids younger than 10 or 11.) When she was seven, she asked to read Twilight, because it fell within her AR range. That was my first YA novel, and I was hooked... (I said, "Absolutely not! You can read it when you're 12.", by the way.)
These days, Emma is almost 10 and I give her a little more latitude. She is pretty much free to read anything she wants in the Juvenile section, with a very few exceptions (I really don't like books that glorify "mean girl" behavior). If she wants to read a YA book, I make sure to read it first. I really don't have a problem with language here and there, and non-gratuitous violence is okay with me. Romance is fine to a point (no graphic descriptions or overly intense teenage relationships). Glorified teen drinking and drug use are a no-no (I sometimes let teen drinking fly if there is a consequence or lesson learned from it). There are definite "No" books, that have content that is WAY too mature (ex: anything by Ellen Hopkins). There are the books that I say, "Okay, but first we have to have a discussion about some topics that will come up in this book." (ex.: Elsewhere by Gabrielle Zevin) There are the ones that we discuss WHILE we read them TOGETHER. She's still young enough that she likes me to read to her at bedtime, so I read discussion-worthy books to her then. (ex: The Hunger Games) Right now I am reading Life As We Knew It by Susan Beth Pfeffer to her. It can be a scary book in a very realistic way, but it is also a great lesson in being grateful for all you have, and realizing what is important in life. Finally, there are the books that are pretty "clean", but a bit more of a challenge in complexity. Those I let her read on her own and she bring me any questions she has at her own discretion. (ex: Matched by Ally Condie and Everlost by Neal Shusterman)
In the end, every kid is different, and they all mature at a different rate. What's right for my nine year old may not be right for yours (I got A LOT of raised eyebrows over reading The Hunger Games to my daughter). The important thing is to remember that the age ranges that libraries, bookstores, and publishers give are GUIDELINES and that the best way to determine what is right and appropriate for your child is to talk to him/her. Then if you have doubts, read it yourself, or go to a trusted source for information. There are loads of blogs out there (duh!) that have reviews and ratings. Look for one that fits with your level of conservativeness, or even better, is a bit more conservative than you are. One website I like is Common Sense Media. They are much more conservative than I am, so I know that if they say "ages 9+", that I can count on it being "safe" for my daughter.