Remove birthday?

Is there a way to clear one’s birthday completely? I’d just as soon leave it blank, but I can’t figure out a way to do so. Clicking the “Reset Fields” button doesn’t seem to do anything.

the birthday question has some legal ramifications.
if you do not want your actual birthday - either as Mon/Day or Mon/Day/Year
just make up one that will make you at least 14 years old

Can’t it simply be left blank? I have not entered anything in this section and my account seems to be working fine. (Just to be clear for legal purposes, I am well over 14.)