he can contact sony https://support.us.playstation.com/app/contact_opt
but without knowing the DOB he will be asked to asnwer the "security question" answer he provided when first signing up, my guess is if you faked his DOB he did not take the security question step any more serious so if he doesnt know that he out of luck
Did you do it like this?
If that did'nt work your options are limited to Sony support only.
There phone number is 1-800-345-7669