I read these books when i was a precocious 8 year old, which is probably a few years younger than the intended audience. As such they blew my mind and probably have a great deal to do with forming my personality as an adult. They are amazing stories of friendship, adventure, distrust of authority and possibly the true meaning of freedom. It's true what Slow Tiger quoted. They are the best mix of epic and nasty.
I checked my ears to see if they were getting pointy out of a mixture of fear and hope for years after reading these books.