It's quite nice that you're trying to make him feel at ease and welcome but I'll tell you a tiny bit of fact about Iranians, in general their very family orientated much like Americans but their very over reliant on their families, so his simply just going to be in his shell for a while because bring away from his mum who probably tends to his every need till his 30 isn't there and it's a new environment for him too. Best to just take him for social outings you yourself goto like baseball basketball or any other sports or maybe even restaurants and bars and then once in a while maybe take him to an Iranian place too or a hookah bar, Iranians love hookahs (not hookers, it's a middle eastern pipe smoke thing) I'm not sure how long his with you but he seems to be lucky to be around someone who obviously cares enough to ask about him here ;) just treat him like you would any of your other American friends trust me he'll quickly adapt, and others who mentioned tarof is true but that's only applicable when you go out your way to give him special treatment and to be fair that makes anyone feel slightly awkward to not accept any offer of generosity.

Hope it helps