To me, the sexual elements might be more problematic for younger readers than the language, although modern television (I got rid of my TV five years ago, and haven't looked back since) features ample coverage of both.

The book uses language that kids hear (and use) in school. However, there is a lot of sexual fantasy on Junior's part, including several vivid descriptions of masturbation and sexual arousal, which may be just a little too mature for preteens. There's also a lot of alcoholism and physical violence, so I would reserve this for the teenage crowd.