masterbate....15yr old boy

ok so i have masterbated for about a year and i have had no problems, i was looking at a porn website and a girl was giving a hand job to a guy but his foreskin was sliding up to the tip of his penis. when i tried this my foreskin wouldnt move that far and it wouldnt slide verry far, is this normal that it wont go so far do i need to yank harder or does it become looser or something when im older...just wondering...thank you
o and im a boy and im 15