Let him explore his own interests. The most important is that he gets into the habit of reading and enjoys the experience that books provide, so it doesn't matt

Let him explore his own interests. The most important is that he gets into the habit of reading and enjoys the experience that books provide, so it doesn't matter if he reads sci-fi, fantasy, philosophy, science books. You can of course recommend him some books, genre or author, but it should be his decision wether to read them or not. You could recommend him some divulgation books like "A brief history of Time" by Stephen Hawking, "Parallel Universes" by Michio Kaku, or "The Dragons of Eden" by Carl Sagan, they're all quite enjoyable.