Many people choose the default settings when entering their birthdate information into Facebook, and as a result the day, month, and year of their birth is displayed in their profile. You can preserve some privacy and change this default so that only the month and day appear.
First, log into Facebook and click on Profile. Then, click on the Info tab under your name, and then the Edit button next to Basic Information. Select “Show only month and day in my profile”, and scroll down and click the blue “Save changes” button. Here is a screenshot:
With these settings, only the month and day of your birth will be displayed in your profile. The year will not be displayed.