I was an advanced reader. My advice would be to get a membership for your local library and let him decide what to read for himself. It doesn't matter if he reads a novel in 30 minutes if he enjoyed it (although it gets to be a PITA to be constantly having to find new books). Ask the librarain to teach him the basics of the dewey system and what a bibliography is and he'll be able to use any library in the world.
My parents never bothered telling me what was too old for me so I ended up reading all sorts of 'unsuitable' literature and remaining blissfully unaware of how adult it was.