how old r u ???i think that u shouldn't try to stop it, whenever i masturbate i just start rubbing my penis faster and faster and pressing my **** harder as much as i can. i cannot control myself, it feels so damn good when it is exploding out of your **** !!! and then when its coming out, i start rubbing it over my **** and again start over again till its all out, and then i feel guilty about it that y did i do it !!! wtf, i don't know y !!!
Well I never heard a person having trouble by stopping,but whenever you do it regularly in many years, remeber that when you press hard you're actually compressing your urethra to prevent flow,which means that it would go retrogade either in your bladder or epididymis,so you'll be prone to UTI or inflammation of your urethra.
Hope this helps.
It's okay to start/stop if you feel that penis is about to ejaculate but once you go pass the point the ejaculation starts shooting out you are not suppose to stop it from coming out.