If you're asking whether "seriously" nine year olds aren't allowed to read it, yep, even at least one gifted kid, in my ds's case. My ds turned 10 yesterday and I would not let him read it. Ds11 (12 in April) read it recently after much discussion. They also DO NOT play violent video games (Wii, which is all we have, isn't that violent to begin with, and certainly not the games we have). We do choose to set limits based on what we feel is appropriate for our kids. Neither ds has watched a PG-13 movie. You really can't make assumptions so easily (that every single kid is playing violent video games). I read enough of the book to know that it didn't appeal to me (ds11 finished it, but chose not to read the sequel). Not everyone is ready for that kind of storyline. I respect your decision to let your son read it, but you should also respect that some kids (frankly, I think many) are NOT ready for it in 3rd grade.
