Torn..

I'm young and currently in a committed relationship. He's 24 turning 25 this month and I'm 20. He wants to start a family within this year but I'm not ready yet kind of. I want to join the air force for about 4 years, By time I get out I'll be 25 hell be 29 or so. I don't want to wait that long to have a child but I don't want to have a baby to early. If I really enjoy being in the air force, I will stay for the next 20-30 years. If I get pregnant while in, will they discharge me? Can I returm.