1. Establishment of a World of Warcraft Account. A. You may establish one (1) user account (the "Account") with which to play World of Warcraft by accessing the Service pursuant to the terms, conditions and restrictions contained in this Agreement. In order to establish an Account, you must be a Natural Person, who is the age of majority in the country where you are a citizen.
I'm not sure if Blizzard would give his mother access or just shut down the account, but she could certainly contact Blizzard's Billing and Account Services dept. and find out.