I am 21 years old. Bro if your foreskin isn’t going back by much but it is erecting to the full limit then you don’t have to worry because the makeup of the foreskin is purely genetic. For some there may not be much skin and for some there may be more skin.
If your penis is getting fully erected and fully hard then I believe you shouldn’t worry much.
But if you can’t get hard enough then there may be some underlying medical issue for which you need to consult a doctor. But considering your age it shouldn’t happen to you so soon.
Hard core fappers some times face the problem of loosing their libido, but if you are not one of them then there is nothing for you to worry about.