I have been meaning to comment on this thread for a week or so, just got down to it. I am getting on in years, but some of my life experiences may be of interest to some.
When I got married I had a completely unretractable foreskin. my first wife had had a previous BF who was retractable, and often tried to retract mine. She persuaded me , on the advice of her mother, to at least see our doctor, who said that it may resolve itself over time and to wait until we had been having sex for a year or two. He did give me steroid cream to put on the foreskin twice a day. After a couple of months, the foreskin did become much looser and thinner and retracted enough to show some of the gland.
Things stayed the same for several years, during which tie I got divorced and ended up with a new partner. She was much more interested in my cock and enjoyed stretching and playing with it. During sex I remember she once or twice she would put her hand between us and hold my foreskin back as tight as it would go often the entire gland would retract out. this was pleasurable but almost unbearable, and afterward it would be difficult to get the foreskin back over the gland. The skin got stuck in the rim under the gland
I was hospitalised some time after that and needed to be catheterised. during that stay in hospital the foreskin was cut open enough to reveal my gland and also to enlarge the hole at the tip to get the catheter in. After that, whenever I had an erection. the gland would come out and retract a bit but it would bend the gland downwards.
Over the years my foreskin has become tighter again. I can retract all the way back with ease and he skin goes forward easily. I recently needed medical advice and was given steroid cream again to treat a rash on the gland. at 70 my foreskin has loosened again.
I do agree with circhead, It is the frenulm that stops the skin going back under the rim.
Having watched a fair bit of porn, I think the way a boy leans to masturbate is relevant to how his cock develops. I always rolled the gland inside the foreskin. I never tried to pull the skin back . It was considered dirty to touch myself my mum never said anything to me about hygiene.
Just my two-pence worth.