My Dad got a Dx of severe dyslexia at age 60.
It wasn't that he didn't have dyslexia before, but that he had developed coping strategies to enable him to manage and get through life to an extent, until he progressed so far into his career that the demands of his job got him the threat of a disciplinary and an OT referral which led to his dyslexia assessment .
I think one way or another, IQ must play a part in how much someone can teach themselves to fit in/adapt. My Dads turned out to be very high (at least that's what e told us -lol)