An 18-year-old mentality regarding sex? Unfortunately this is not very unusual. I know a lot of men who don’t develop even that far. Moreover I doubt Mother Nature intended them to go farther.
(Our Father in heaven being a whole different matter.)
As someone who works with young people, including those whose girlfriends are pregnant, if there's one bullsh*t myth I'd love to erase it's that men are the only ones who are immature about sex. These young women I'm currently dealing with knew PRECISELY what they were doing when they got pregnant.
Sorry to see this liberal attitude about men and sexuality is accepted as a matter of course even here. It's a pile of crap.