I'm 19 not pulled foreskin back can't hurts. Can only pull back when flaccid not erect when I get errection after pulling back on flaccid it doesn't get bigger like normal... I should probably stretch it gradually, right? Cheers for any response!
Yes, stretch it!
Your foreskin should slide easily over your glans while erect. It'll make intercourse more pleasurable - and masturbation can be too.
The glans will be very sensitive at first. This is normal and will decrease in time.