I used to suffer from premature ejaculation when I was young. I think we're basically designed to do that to ensure that we impregnate the girl. But her pleasure is also important so we see coming quickly as a problem. I tried numbing sprays but I don't like them. Eventually I got my head around the problem and I see it as:
A) High libido because your testosterone is probably as high as it'll ever be, so you get very excited about and by sex.
B) High sensitivity on your part because you're young and healthy.
C) Anxiety caused by being eager to please your lover.
As a young man you shouldn't really mess about with your testosterone, so that rules out doing anything about A.
I don't like desensitising sprays/condoms because they spoil the nice feelings, so I don't think you should do anything about B.
C is where you can really tackle the problem. I'd like to start by saying that trying to think of something revolting during sex is a pretty horrid idea, and if I was your gf I'd be pretty disturbed by the idea that you're thinking of your granny as you fuck me. Ew!
So what can you do? Firstly communicate. Talk to your gf because a problem shared is a problem halved. She wants to help you have great sex too.
Lets go back and look at A and B and see if we can turn a problems into opportunities. You're young and fit, so use it to your advantage. You should be able to reload and go again much more quickly than someone of my age, so why not make use of that. MAKE SURE YOU'VE HAD PLENTY OF SLEEP, AND TAKE YOUR TIME OVER SEX. Have some relaxed sex with your girl, maybe do oral on each other, because it tastes nice, eh? Give her an orgasm. Straight away you'll reduce your performance anxiety by doing that, and then at least you'll have proved to yourself and her that you're not a selfish lover - in fact, you're pretty damn good. After a break you'll be up an ready to go again. Second time round you'll have far less of a tendency to come so soon.
My next advice is to do with technique. Let your girl know that you'd like her to try to relax and let you dictate the pace. Instead of spectacular long and fast strokes, bury your cock in her pussy and gently nudge her with the root. Go at a pace that you know keeps you the right side of orgasm. If you feel you're getting there too soon, slow down and maybe stop to get back into the 'safe zone' where you don't feel in danger of coming immediately. Keep at this and she'll learn to let her orgasm build without the need for fast tense action. It'll take a few sessions but by trial and error, but they aren't really errors, because it all feels good and if you lose control and come your gf knows that's only because you love the feeling of fucking her so much. Eventually, she will come on your cock and her pussy going wild will trigger your own. That's what we're talking about isn't it? Keep the faith. It will happen.
All the best.
