Lol-a lot of guys are like that. I'm almost 26 and my hubby is the same way. I keep having to tell him "do you realize I am due in 3 weeks?" i'm freaking out while he's all happy that the new dave chapelle is out on dvd.
It's hard when the baby's dad is young which i'm guessing he is in your situation, hopefully things will change once you have the baby.
I think because we are so close to our baby while it is growing, we realize a lot more. While we feel every little thing, to them we have a big moving belly.Lol. Ususally once the baby's out things get better as they have something to actually see and feel themselves.
Good luck and don;t worry, i'm sure all will be fine.