The profile information page in the User CP is here:
http://www.oddworldforums.net/profil...do=editprofile
The link to that page is broken and doesn't show up in the Industrial and Native skins, you have to use Munch's Oddysee or Honeybee to find it. The direct link will work in any skin, though.
The profile page says to contact an administrator if you need to change your birth date.