Eighteen or older, lasting longer doesn't come magically, you have to learn some techniques. The most effective technique to lasting longer without resorting to two condoms is to practice through masturbation. Set aside some privacy time, masturbate gently using a light touch, as light as the grip of a woman's vagina, and feel how a tingling sensation gives you warning that you're getting close. Stop or ease off, and then start again, and keep doing this until you ready to come. Practice this technique, and then try it with your girl. When you feel close to coming, slow down or stop, and then start thrusting slowly again. Not too fast after reaching your peak or you may lose it.
An adjunct to this is to build up your kegel muscles, these are the muscles you squeeze if you want to stop urination mid-stream. Exercise these muscles for a couple of minutes a day, and when you do your masturbation training, squeeze hard when you get close. This will stop you from coming. During intercourse, squeeze the same muscles when you get close.
This is basic tantric sex training. This isn't how to do non-ejaculatory sex, but this is what men who have been trained in tantric sex do to prolong intercourse.
Women typically don't like to be fucked for an hour, or half an hour, or anything like this, so don't overdo a good thing. The ideal time for most women most of the time is from seven to 15 minutes, and a recent survey showed that a majority of women prefered three minutes to thirty.
