Why Change Or Hide Your Birth date? There are a few reasons why a Facebook user might want to change their birth date or hide it on Facebook. The first one is privacy, you are more likely to be the victim of identity fraud if you make it known the exact date of your birthday. The other reason might be if you are a minor (under 18yrs) on Facebook you may not want anyone to know that you are for cyber safety reasons. The third reason is that your teen has lied about their age on Facebook when setting up their account so that it is in fact an adult account (over 18yrs) rather than a minor account, and you may want to correct the birth date on their account so that they are getting the stricter privacy settings that a minor account provides.