To enable the customer to add the date of birth as optional, you just need to configure the DOB correctly ...
Go to the Configuration ... Customer Details ... and set to: true
Date of Birth
Display date of birth field during account creation and with account information
NOTE: Set Minimum Value Date of Birth to blank for not required
Set Minimum Value Date of Birth > 0 to require
Now go the the Configuration ... Minimum Values ... and set to blank, not 0 but blank as in nothing in the input box, as instructed:
Date of Birth
Minimum length of date of birth
Now the date of birth will display, but is not required ... :smile: