When did you learn to read? I started pretty early, either in the late twos or early threes. Of course, I didn't start talking until only a few months before that, and wasn't elocuting correctly until I was five, so I guess that balances out.
I'm trying to determine whether quickly learning to read is more of an N/S thing, or an P/J thing. The N/S thought is that N-users might notice the connection between written word and speech much more quickly, while S-users might require the connection to be more explicitly pointed out. Consequently, this might mean that the former don't necessarily sound words out in their head when reading, while the latter do, since there's much more of a concept of a written word representing a speech pattern, rather than both the writing and speech indicating a given concept.
The P/J thought is that extraverted Sensing/intuiting will more likely pick up on the connection between language and writing, as there is a greater sense of familiarity with the outside world. For example, an Se user might learn to read easily when a written word is pointed out, and then told that it means a given spoken word. Ne will just put two and two together. Meanwhile, introverted Sensing/intuiting might have a harder time with this, given the introverted nature of their perceptive functions. Si will have had to internalize the rules for the connection between written words and speech, while Ni will struggle with there being any true connection between writing and speech (which of course, leads to a later fascination with language, particularly in the formation of artificial language)