Well... excessive masturbation can cause this, but it can happen as well without that. Young guys with performance issues statistically respond strongly to therapy, meaning there's often mental blocks.
Foreplay isn't just for the woman. You need to be in the moment and believe it can happen. Simply being anxious about it can prevent it from happening. Building good sexual tension is both mental and physical. You need to understand how to prime yourself, and also understand how she can sensitize your body. For ex... my lover has long hair... she knows if she straddles me from behind and rubs my back, I like it.. but when she drags her hair over my skin, it kicks up the sensitization a notch. Stuff like that can make a difference.
Also, some positions can make a difference. If someone put a gun to my head and said "have sex and an orgasm now" there are a few positions I would favor... not to mention there are some stims that can be done during sex that can push me over the top. Her fingers gently tugging at your guys, biting at the ears or neck late in the game (not too early, save it for later)... there's even a few positions I like because I can get my hands on her better than "straight on"... some side positions always get me more stimulated than missionary... or at least its different stim, and changing things up is good. So understanding that there's more to intercourse than just "in, out, repeat"... that your skin is your biggest errogenous zone so use it all, and your mind is one of the most powerful enablers or disablers to reaching orgasm... its all important.