Have you tried the delay method where you hold the base of his penis during sex?
A man cannot ejaculate if the bottom of his penis (the fluid tube) is held tightly against his penis' shaft.
delaying condom, delaying cream, hypno-therapy, pills from the doctors, herbal remedies, you try these things when you are with the partner.Don't try these to masturbate.
If you masturbate often and come fast during then you need to lay off. If you do so what happens is, your body and brain is now trained to come quickly. Stop masturbating for about 2 weeks and you will notice a difference.
You can practice Hold off method.When i started out at your age i could only go 2 minutes and i hold off when i am at the peak point i withdraw and resume and again when getting to that point again withdraw and again.practice this sure you will improve.Now i can go all night as long as i want,with my partner.I think when you are with your partner you will be much better.so don't worry.