I spent about 3 years locked out of my Yahoo account, because I'd forgotten I'd set my DoB to 01/01/1900, and one of the unlock questions was what's your DoB. :

I spent about 3 years locked out of my Yahoo account, because I'd forgotten I'd set my DoB to 01/01/1900, and one of the unlock questions was what's your DoB. :) Once i got back in (after suddenly recalling the password!) i tried to change my DoB so it wouldn't happen again, and found I couldn't.