Generally everyone is correctable to the required standards - there are people who have -25 eyesight corrected to 6/6, so it wouldn't be something I would get too concerned about.
Usually errors of refraction stop getting worse when people stop growing, at around the age of 21, but there are cases (not sure how common it is) of "Pathological Myopia" which means that the eye doesn't stop growing, hence making the error of refraction worse.
I shouldn't worry about that though.