Both of my DYS have loved those books, but we didn't start with them until age 7...and both of them ended up getting hooked and reading them all rather quickly. I'll admit, that even at age, I was a bit concerned about the content of all books after Book 1. I think it is really about knowing your child.

Can you just "neglect" to tell him about the other books for a bit? So many great books out there...can he read some others first and then you can circle back a little bit later?

BTW, both DC also found the books worthy of re-reading wink.