There are topics that 14 year old kids read that are not appropriate for the younger set. DD9 switched to the public school this past year, and the teacher quickly noted her reading skills. Lexile level (reading with comprehension) around 9th grade. However, teacher noted that while she can read (and understand) books at that level, that doesn't mean she should be reading just any book at that level. Teacher screened what she was reading to ensure the content was appropriate.
There are even rather low lexile books that deal with very mature topics. For example, there are books that deal with the Holocaust that are in the lexile level 400-600 range. That doesn't mean that 7 and 8 year old kids should read those books, only that they would comprehend.
The good news is that there are plenty of books out there, and many have appropriate content. My middle kid often laments the push (by teachers I guess, it wasn't me) to read higher level books at a young age. She says that she missed out on a lot of "classics" that most other kids read, and she will go back and read them someday (perhaps when she is an adult - she is 16 now).
Good luck with your decision.
