..you are speaking of a very small minority.. the vast majority of kids who cannot read or are functionally illiterate is due to teaching methodology. By age seven, yes...it's a minority. Most kids hit it in the mid 4 to late 5 year old range, but it still exists as late as late-7s. By beginning of 7, things like dyslexia are far more common problems.
I meant.. that it is a very small minority that have reading problems due to some abnormality.