Some states will permit early entrance to kindergarten if the child has high ability and will be the correct age within a certain number of days of the legal cut-off date for entry to school. These early entrance requests must be backed up with professional testing results, and the child must be mature enough. However, you may not be considering this option.
My opinion has always been that you are only a young child once, and a child will be in formal education a long time. Why rush things? A preschool that allows your child to read at his own pace (even if it's above everyone else's), that encourages word-play and writing-play for learning (instead of only unstructured free play), and that has lots of books available to supplement his books at home, will be a good school for him. At this stage, the majority of his actual reading fluency will progress at home. Your goal is to locate a preschool that will not impede his efforts.
A final suggestion: Definitely encourage fine-motor growth through crayon and pencil fun, mazes, dot-to-dot books, scissor activities, etc. Many young, gifted boys are better at reading and talking, and tend to neglect the writing side of learning because it's trickier. Now is the time to encourage this manual activity as it's hard to improve on this when kids are a few years into school. Good luck.