Comment by meiraleal
I don't think there is a rule for that? At least not in my case. My eyesight got worse really fast out-of-nowhere when I was like, 15 years old? And since then it didn't change anymore. I got myopia, after a few years of too much computer screen (the old CRTs).
While there was a suspicion of eyesight troubles in my late teens, it really kicked in during a period I was working on pretty crappy screens, that was in my late 20's. It's not much but enough to give me headaches when not wearing them.