My kids have all been early readers. My daughter was not as blatant as your son, but she was very shy about demonstrating reading ability in front of others. Her next oldest sibling was a spectacular reader; using reference guides and reading adult non-fiction at age 2.5. Although we never made a big deal of it at home, others were exclaiming all the time over his reading ability. His Montessori director referred to him as a prodigy during a school assembly, much to my chagrin.
I think she was nervous that she wouldn't measure up, and she does have a spot of trouble with perfectionism. She played dumb so well that she would read entire books to me but then pretend she didn't know any of the words when Grandma came over and asked her to read the same book. She came out of hiding around the time she turned three, and by the time she was 3.5, she was reading Black Beauty. These days, she is a more avid reader than her brother, and frequently reads my books. She's seven.
My youngest is able to read, but doesn't like to read aloud. She's been reading books for almost a year, and does quite well at reading her way through various computer games. I figure as she becomes more confident, she'll be more overt about it.
FWIW, I read bedtime stories to the kids until they decide they are done with it. For my sons, this happened at age ten. For dd, it was six. My littlest one still tries to talk me into reading longer every night! We tend to do about 20-30 minutes per night.
