As much as I enjoyed the Lioness quartet, there are references to sex. Just be advised if you do go down that path.
Quite right. I had completely forgotten about that. However, if memory serves, the Immortal series doesn't. And I know that the Circle of Magic series is free of it.
I'm an avid fan of Tamora Pierce and began reading them around the same age as your nephew - as long as he doesn't mind female heroines, than the "Tortall Quartets" (which is Lioness/Immortals/Protector of the Small series, plus some new ones out lately) are very, very good. They're intended for mid- to older teens, and while they do contain some references to sex, there is nothing blatant or scandalous about it. It looks more at the emotional side of the relationship and how it affects the character. [Which could be a good kind of educational.] So depending on how mature a reader your nephew is, you may want to wait a couple years.
And yes, there are references in both Lioness and Immortals - less so in Protector of the Small, but still there.
You may want to start with the Circle of Magic series, which was intended for early teen years, even pre-teen. There's no 'mature' references in it and it's a great series with humourous, well-written characters and a compelling storyline. There's also a sequel quartet for it too, I believe, called the Circle Opens.
Aside from those, I totally agree with those who mentioned Lloyd Alexander's Prydain series - excellent, excellent read. David Eddings - depends again on how mature of a reader your nephew is. It's a fairly straightforward [and clean] storyline and I read them while I was young, but it was written for an adult audience.
Have you tried some other classics, like the Chronicles of Narnia? I would mention Harry Potter, but I've never read them so I don't know what kind of references there are in them.
