why would there be and funding available for him to do what he wants post graduate - unless he approaches a company to sponsor him. people in this country dont get any funding for post university studying, unless its through their job for example let alone university studying, (where lots of people dont get any funding for that and have to pay course fees etc)
if he is a graduate with a university degree, why cant he get a job now and do the course part time, thus enabling him to fund or part fund himself?
are you asking about government grants etc? Again if so, why should they when he dosent pay any taxes here (and sounds like he may not have done all his life because he was too young). If he has been residing in america for some years as your question implies then he might not even be entitled to nhs care if he came back here, let alone any other state help.
He sounds like he is probably old enough to understand the value of money so my advice if you cant afford it is to say no to him! and let him learn you cant have everything you want in life