In terms of fantasy, the following come to mind:

- obvious, but if he hasn't read it yet: Lord of the Rings
- His Dark Materials by Philip Pullman - not entirely sure there on whether he'd get uncomfortable, there's nothing that's truly that shocking (other than the religious matters if that's an issue for you), but there are some scary moments
- Belgariad and Malloreon by David Eddings should work (I like Elenium and Tamuli too, but those are even worse in terms of body count (not of important characters, but still - it's not that it's graphic or anything, but when you stop and think about it, the protagonists really do kill an awful lot of bad guys))
- again stating the obvious, but Wheel of Time?
- Terry Pratchett, he likely wouldn't get all of the humour, but much of it at least
- some of Gaiman's books (not American Gods though)


Outside the genre, there are some of the classics that should be doable, whether he'd fully appreciate them is a different question. I'm thinking of To Kill a Mockingbird, The Three Musketeers, Ivanhoe,...

As for more explicitly YA, I remember that when I was that age I loved the books by William Bell (Forbidden City in particular is impressive) and Aidan Chambers. Both are very good at writing for and about kids in puberty or adolescence. Astrid Lindgren and Roald Dahl are perhaps (for the most part) slightly below his reading level, or at least not very challenging, but remain fun regardless, if you ask me. I read a lot of Anthony Horowitz at that age too, but his books are mostly thrillers and horror (age-appropriate horror, but still, can get fairly scary), so considering he quit HP at the Inferi, perhaps best not.