AC, I've read this series all the way through at least three times, great books. This is NOT game of thrones - no explicit sexual encounters, no nudity, and zero curse words. The author has invented some stand in curse words that his characters use, like "Blood and bloody ashes" which is probably the equivalent of saying "son of a bitch", but that's it. There is a fair bit of violence in the books, and several forms of magic, but it isn't terribly graphic. The author mentions for example that trollocs (one of the evil creatures in the book, created through genetic manipulation in a long ago era) eat humans, but he never (that I can recall) actually describes them doing so.
The characters in the books start out in a small village which gets attacked, and they find themselves swept up in a continent spanning adventure which at first mostly involves running from bad guys, seeing lands they had always dreamed of one day going to, and slowly learning why the bad guys are after them. Along the way they learn a bunch of lessons, including self reliance, that sometimes love is complicated, the burden placed upon individuals in leadership positions, and that the people you choose as family can be as important as the ones you're related to.
The series is very, very long, as Ash mentioned. I'm not sure how long the Harry Potter books are, but several books in this series push upwards of 1,000 pages, so he will have no shortage of things to read for a while (there are 13 books in the series). With that said, there are some options to ease into the books should you wish to make them more approachable. Book 1 was split into two shorter stories a while ago, in an attempt to make them less intimidating for new and young readers to jump into. It sounds like he might not need something like this, but it is an option.
From the Two Rivers: Eye of the World Part One and
To the Blight, Eye of the World Part TwoThe first book was also made into a series of graphic novels. While it is cool to see the story hand drawn in these books, only book one is available in this way, and it will be quite expensive to get the set. This might be a future gift should he really enjoy the series.
Wheel of Time Graphic Novel, Volume OneI cannot recommend these books enough - in a world full of dark and gritty fantasy books, The Wheel of Time is a breath of fresh air. I'm sure your little guy would absolutely love the series.