The basic thing he has to learn is to spot the signs that he's about to come and then, if he doesn't want to do so just then, lessen the stimulation so that he doesn't. The fact that he can last five minutes says that, if he learnt this, he could do fifty or any other time.
Have a read of Bernie Zilbergeld's 'Men and Sex' or 'The New Male Sexuality' - amongst dozens of them, there's almost always a listing on Amazon of one of them for 1p + postage second-hand. Amongst much else, it has a good programme on how to learn this.