Currently, there’s no way to update your date of birth once your Kik account has been created.
If your Kik Live profile displays the incorrect age, you may have entered an incorrect date of birth when creating your Kik account or you may have an older Kik account and signed up before your date of birth was a required step in the registration process.
If you would like your Kik Live profile to display the correct age, you will need to deactivate your current account, create a new Kik account and select the correct date of birth during registration.