I am 13 and half and have pubes. I can pull back my foreskin when my penis is flaccid . When my penis is erect i can pull back my skin but when i let go the foreskin rolls back and covers the head of penis. Because of this i cannot masturbate with my skin pulled back.
If your foreskin rolls back and covers the head of the penis, it simply means that you have a long foreskin.
The foreskin is an asset and highly beneficial. A long foreskin is more of an asset and more beneficial than a short foreskin. Moreover, the ancient Greeks considered a long, tapering foreskin to be a sign of male beauty. The long tip is called the akroposthion.
Long full-length foreskins will not auto-retract on erection. Only inadequate short foreskins will auto-retract. For your skin to go back, the foreskin has to be wide enough to retract over the head.
If your foreskin is wide enough, it will retract if it is shorter than the erect penis. If it is longer, then it will never retract by itself but may be pushed back, however, it may not stay back. Some longer foreskins spring forward again when released.
When a long foreskin is manually retracted, it gathers in folds at the base of the penis. The folds want to unfold and push the foreskin forward back to its normal position. A long foreskin is likely to slide/roll forward to recover and protect the glans penis when it is released. Some men simply cannot keep the foreskin retracted. This is not considered to be a problem.
The long foreskin provides superior protection to the head of the penis and keeps it soft, smooth, and sensitive.
The long foreskin may improve the sexual experience because of its superior gliding action. The long foreskin also may have more pleasure nerves.
Don't believe what you see in porn videos. Most guys think the best way to masturbate is with the foreskin over the head.