Can't remember when I couldn't
By the time I was in kindergarten I was reading. By second grade, when they expected everyone to be reading well enough to do book reports -- on the little 25-page children's books -- I was reading Hardy Boys books. Some of my book reports seemed to be longer than the books other kids were reading. The school library ran out of them before I finished the grade.
I think I remember my mother saying once that my older brother (two years older) read to me before he was in school, so we both started really early. She doesn't seem to recall how early he started. But I am sure that my parents made a conscious decision not to "baby talk" to us, so our verbal skills were definitely advanced. Fluent conversation with adults by the time I was ~3 or 4.
