Yeah it's extremely common, especially for a guy who's only ever really known his own hand. You could try going down on him first and then having sex - he's likely to last longer on his second go. He can practise lasting longer on his own by bringing himself to the brink of orgasm then stopping and squeezing the base of his penis. The more he can control how quickly he comes by himself the better he'll be at doing it during sex. If he feels the pleasure is too intense you can always go really slowly, and get him to think of something really unsexy (I hear the thought of Anne Widdecombe naked on a pogo stick works quite well) or practise the stop-start technique (pretty self-explanatory I hope). If all else fails there are topical applications you can use that contain a mild anaesthetic - in fact I'm pretty sure you can buy condoms that have an anti-climax solution inside them. Hope this helps!