Read what Hukora said above-
EDIT: After looking at this guide again, I realized that the guide might not be correct. To my knowledge, you will receive your birthday gift email on the date of birth that you entered when registering for your in game account (which cannot be changed). You can set a different date of birth on your forum account, but the birthday gift email will still only be sent on the date of birth that is stated on your in game account. To see what date that is, click on Account (left sidebar in game screen) --> Profile --> Birthday (right sidebar).