When the minor turns 18, we require him or the adult on the account to close the account & open a new account. If this is not your practice, then you could request the customer provide ID etc and if he did not - close the account. You would want at least minimal info on the minor, now adult individual. (you would probably only have a social for him, may not have a current address, would not have his signature on file and would not have a driver's license/state ID number on file)