Our dd, now 15yo, carried around a DK alphabet/word book nearly as big as her, perhaps starting when she was around 13 months. One of her first words was "readabook." We did help her learn b/c she was so interested, and she was reading pretty well by her second birthday. She has been a voracious and lightning fast reader ever since. She is also very strong in math.

I was concerned about hyperlexia/autism at the time, but she was not diagnosed with either.