I found a post that was over a year old saying that this has to be done by a database query. Is this still the case today? I'm guessing so, since I can't find an option to change it, but wanted to double-check.
I suggest running this query to change all the dob_year fields that are currently showing 1900 to 0. Always backup your database first before running a query....especially for us who just imported thousands of users whose birthdays are now showing them all to be something like a 113 years old.