Hi jamoo,
it's not physical, it's all in your head.
I'm 27...But this used to happen to me. And once it happens you cant stop thinking about it when you're getting into it with a chick. It remains in the back of your head and that's what does it.
Let yourself get into it. Try not to think about the possible limpness. Lol
serious...I would have a couple of drinks before. Not to get my drunk but to get me emotional. This may sound gay but let your emotions guide you, not your brain.
I was always thinking of my next move......Dont! Just go with it and think of how good it will be.
Once you f*** a couple of times without thinking of it you're good to go.
I dont have any issues anymore.