BikerOrNot FAQ - Why does my birthday not show up in Upcoming Birthdays?
Upcoming Birthdays is a list of your friend's birthdays. Since you are not friends with yourself you do not see your own birthday. Your friends will see your birthday if you made it public during sign up.
To check to see if your birthday is public, click "Account" on the top right, then "Edit Account", and make sure your birthday setting is either "Show my birthdate with year" or "Show my birthdate without year".