13 year old with high reading age

Hi all,

My nephew is 13 years old and is an excellent reader. His favourites are usually fantasy/sci-fi, but open to any and all suggestions.

The issue is that he has a high reading age and has exhausted most of the popular options aimed at his age group (Harry Potter, Eragon, Percy Jackson, etc..)

I’d like to get him some books that challenge and engage him, but I’m finding it difficult to ensure they’re appropriate for him – a handful I’ve found are quite heavy on sex/murder/drugs which I’d obviously like to avoid.

Any ideas welcome! Thanks in advance for your help folks.

tl;dr – Suggestions for a 13yr old boy with a high reading age. Nothing too dark/sexual in nature. Sci-fi/fantasy preferred but all ideas welcome.