I think this is disgraceful. It's unclear to me whether these are guidelines based on the material in the books or the difficulty of the books to read, but I'm against it either way. I believe that censorship is ridiculous: if a child is old enough to understand the content of a book, then they're old enough to read it. And children's reading abilities differ enormously: you can't possibly put an age on reading ability. A guide as to how difficult children's books are to read I would condone, but no more.