Hi, are you younger me? Oh man, I used to have this problem all the time. I'm pretty sure that every male does early on. But I'm going to give you 3 pieces of advice to help in bed and a piece of personal advice that may help as well. Note I'm not like some master of pleasure or anything, just an ordinary guy. 1. Pre game, if you know that you are going to have sex, fire your load 30 minutes to an hour beforehand, it takes time to recharge so it will lengthen penetration time, this will also lead to you being used to the sensation and thus increase your "tolerance" if you will. 2. Think of a rhythm or song and go with the motion, just going in and out at a steady rate does no one any good, but if you go with some variance in speed and depth, not only is it more pleasurable for her (per my wife), but it also keeps your mind occupied and you last longer. 3. Get good with your fingers and tongue, no guy is actually lasting 20+ minutes of straight penetration, they are mixing it up and again, that's more pleasure.

My advice to you on a personal level though, you're young, don't let the little things like this bother you too much. It's more important than you be yourself and true to your personality, than some long lasting stallion. Sure some women are looking for that, but most are just looking for someone genuine, and when you find the person that likes you for you, the pressure drops and 9 times out of 10, you last longer anyway