Seems like everybody is right. 99% of the time it's too long a draw and/or hand position on the grip. For draw length you should measure his wingspan (search) and divide it by 2.5. Thi'll get it closer than just letting him draw the bow. Also, generally speaking, when it's close the arrow nock will be straight down from his aiming eye. You can fine tune for feel from there.

As for his grip there is a good tutorial with pictures on Bowsite.com. Click on Features/Practical_Bowhunter/Get a grip. You'll get more from this than trying to interpret what everybody is trying to explain. If he's gripping the bow at all then he's not doing it right. Proper grip will turn the elbow out as the hand is in the grip at about a 45 degree angle. Suggest you incorprate a bow sling if he doesn't have one.