Have him masturbate as close as you can to when you guys have sex.
It takes about 20 minutes to recover and be able to have sex, but he wont be able to ejaculate.
I do this usually 1 to 3 hours before me and my girl do and we always go for over 1 hour when we have sex =)
(and I'm 17 if that means anything)
Here's the deal with premature ejaculation - it's very tricky to cure because it has more than one cause...in fact, you can trace it back to three or four causes and each guy can have a different percentage of each cause, meaning that SSRI's (Prozac, Celexa, etc.) may work for one guy but do absolutely nothing for another; numbing creams might be a miracle-worker for one man but do nothing for the next guy.
So what's the best way to treat and cure premature ejaculation? A treatment plan that tackles ALL of the causes of premature ejaculation.
Proof - http://www.goldjournal.net/article/S0090-4295(02)02075-7/abstract - study conducted to test the effectiveness of creams versus SSRI's versus viagra.
Result? They found the most effective cure was people who used the cream, took the SSRI and viagra and received behavioral therapy, which happen to be all four causes of premature ejaculation (hyper-sensitive penis - cream; imbalanced hormones - SSRI; weak sex muscles - Viagra; anxiety/stress - behavioral therapy)!
Final result - 138 men participate, 136 men reported improvement - a 98.5% success rate!
Do the research for yourself and I am positive you'll come to the same conclusion...premature ejaculation is a multi-faceted problem that requires a targeted approach.
Good luck!