You have to be use Male as your gender in order to use this function.
  1. Logged into MummySG
  2. Click on UserCP (top left hand corner)
  3. Scroll all the way to the end
  4. Click on Group Membership on the left navigation panel
  5. Check on Identify me as a member of this group (Daddy)
  6. Click on Update Display group
Also this is a fixed user title regardless the number of your posts

Thank you,