I don't remember learning to read, or a time in my life where I couldn't read at least a bit. As best I can figure I began reading before my episodic memory fully developed.

I do wonder how I managed to learn anything just by reading on my own though. There were certainly words and concepts I didn't understand (I have a vivid memory of reading a childrens science book that explained the big bang, and misinterpreting it as 'the universe started when the sun exploded'. I noticed the logical inconsistency but didn't pursue it), but I can't think of any instances where those gaps in my knowledge were filled by someone else and I had an 'aha' moment of understanding. I guess we do a lot of learning without realising it.