How to Change Your Birthdate on a Yahoo! Account
To reset your password using your security question, or retrieve a forgotten Yahoo! ID, you must first confirm the ZIP code, country code and birthday listed in your account information. If the birthday you listed is incorrect, you could be locked out of your account and unable to reset a forgotten or hacked password.
Navigate to the Yahoo! website. Click "Sign In," and log into the account containing the birth date you want to change. You are redirected to the Yahoo! homepage after signing in.
Click the arrow next to your name at the top of the Yahoo! homepage. Select "Account Info" from the drop-down menu. Re-enter your password to verify your identity.
Click "Edit Profile Details." Click "Edit" in the "Basics" section.
Select the correct month, day and year of your birth from the drop-down menus. Click "Save" to save your changes.