[Inziladun]

The Hobbit works for all ages, I think. It can be a bit grating in its childish tone at times, but just when one starts to think of it as a "children's" book, it comes out with a very mature theme like Bilbo's mercy toward Gollum, or the complex foray into morality and property rights with Bilbo's "stealing" the Arkenstone in the hopes of avoiding senseless conflict between people who ought to be friends.
It's obviously of an overall lighter tone than LOTR because the stakes are apparently not as high, but I think TH is needlessly maligned by a lot of "serious" Tolkien fans as being a subpar ME work.
In short (too late), it's at least as suitable as things like the vampire books that are so ubiquitous in the teen sections. And the moral underpinnings are a good lesson for anyone, regardless of age.