Your Date of Birth is shown or not shown on the position certificate, this is based on the position setting being set to TRUE or FALSE by the system admin.
Only an Organisation Portal user is able to hide this information for you. You will need to contact your Organisation Portal user within your company to have this enabled or disabled.
This is because if the setting "CertificateShowDOB" has been set to TRUE by the the system admin for a specific position, the position certificates that are generated for workers will display DOB on the certificate.
If it is set to FALSE, no DOB will be shown in the position certificates.
The Organisation Portal user can access this at the following:
Main menu > Positions > Manage Positions > View Details for the position that has this setting enabled > Manage Workers for Position > Certificate