The big three that I remember reading very early were the unexpurgated "Gulliver's Travels" by J. Swift, "The Fellowship of the Ring" by J.R.R. Tolkien, and "The Dying Earth" by Jack Vance. I think I read Gulliver before age 6, and all of these before age 7. I don't remember reading any books prior to Gulliver but after the first book I read on my own, "Little Bear" by Sendak. I must have, though. I know I read the other two fairly soon after Gulliver, but it's hard to remember.
I don't think I was necessarily too young to read them content-wise, though there are some off-color/racy parts in Gulliver. I think that "The Dying Earth" probably encouraged a love of post-apocalyptic yarns, and the bleak and fantastic in general. To this day Jack Vance is one of my favorite writers. I don't know that Lord of the Rings changed me much, but boy did I love it at that age.
