If he can pull 60 lbs, then you can buy him a bow that will serve him until he has his own money to upgrade, with many great choices. If he can't pull 60 yet, then most likely in a few years he will want a bow that pulls in the 60-70 lbs range so that should factor in to wehat you spend.

You can also often get a 'custom shop' bow for a few dollars more from all the major manufacturers that is a tweener, such as my Hoyt that is 55-65 lbs.

Draw length will obviously also be an issue, so getting a bow that has a few extra inches draw length to add would prolong the bows life for your son.