Not necessarily, but that's one of the dirty little secrets: guys with really long penises rarely get them all the way in a girl, because vaginas just aren't that deep, and because he'll be bashing the hell out of her cervix and hurting her if he tries.
I worked with a guy who was known to be huge (I never saw it myself, but he whipped it out in front of other people I knew, who all confirmed its size), and he actually had a lot of trouble keeping girls, because they couldn't have sex with him comfortably, a fact I heard myself from 2 different girls he'd been with. I had to explain to him what he was doing to these girls, and he had to learn not to thrust too deeply to prevent from hurting them.
So, don't be afraid to speak up if he's going too deep, or to explain to him that he can't try to go all the way in and can't bash your cervix all the time. If he doesn't know already, he'll have to learn to control himself.
nope... vaginas are about 5 inches deep
so good luck with that
Finally getting some black dick