I could read Green Eggs and Ham at three, but really I had it memorized.
Both my daughters could read at four, but my oldest was more interested. She was reading chapter books in Kindergarten and read the first Harry Potter in First Grade. Her first 'real' novel, as she says. My youngest lagged about a year behind her sisters schedule. Now in their teens they are both voracious readers. They did have some problems with the Accelerated Reading program, though. Many of the books they wanted to read were not in the program, or were so advanced that they were not allowed to take the tests for them in their grade level.
On a side note, I found books boring for many years and stuck to comic books and encyclopedias well into high school. My parents provided me with numerous sets of encyclopedias and I would read them cover to cover, one after the other. One set, Master Plots of Masterpieces, allowed me to test high in my AP lit class without having to read those 'boring' old masters. The book that really opened up reading to me was The Red Pony by John Steinbeck during my sophomore year.