i'm also a virgin, and 19. so don't worry, there's no rush.
because there's no rush, if you want to make love and not just have sex, the criteria are always the same, no matter how many times you've made love. it should be about whether you love the person. i think that if you are intensely attracted to someone, it counts too.
having sex is different from making love. that's just a decision to achieve an orgasm.
it should be your choice as to which of the two you want to be your first. if you think you love your girlfriend now, go ahead, only after talking with here and hearing what she wants. if you don't love her, well, i wouldn't have sex with her. if you want to just lose it, find a random hookup at a party. if you want to enjoy it and grow from it, find someone you really like.