My girlfriend and I just had sex for the first time last week. We have done it several times since then but I still havn't been able to last long enough to let her reach orgasm.
How long before I will be able to do it good enough to help her reach climax, and are there any tips that can help me last longer and help her reach orgasm.
Maybe never. About half of all women never, or very rarely, experience orgasm from penile thrusting alone. Many of us require some extra stimulation.
At your age, you have plenty of time and recover quickly enough that you two can figure out what is best for everyone. Stay safe.