I'm always on the side of waiting, not pushing my boys into anything too much for them. Of course, I also don't let them automatically watch PG-13 movies when they turn 13 - I always check them out first. And before they are 13? No way. I also didn't let my oldest boys see Rated movies before they were 17, even though ALL their friends were allowed to see them. And they have always had the earilest curfew of their friends. So yeah, I'm a mean mom, so take my opinion for what it's worth.
My 2 13 year olds have not yet read them, but I would let them. One has read the Percy Jackson books, the other one has never been much interested in stuff like that.
I agree with everyone else - read it first, then decide.