Well mentally your son will be more developed than some other players I've encountered.
There's a profanity filter that comes standard with the game, and also as mentioned before you can put people in the ignore list.
Other than the amount of time required to do some parts of the game, there may be some difficulty for your son to get a good grasp of all the games functions (the Auction House and trades between players, various traveling methodes etc.).
Basically I think it comes down to your sons ability to handle setbacks, time and the vast amount of options.