Since you don't allow children on your website at all I would personally disable COPPA Compliance altogether (this is only needed if you're going to be allowing them).
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Alternatively consider adding this plugin:
https://community.mybb.com/mods.php?action=view&pid=808
Quote:This plugin will add options to the registration form for users to enter their date of birth.
You can choose to require a full date of birth, just a day and month, or make it fully optional.
You can also choose to deny users under a certain age.
^ With this one you can ensure they are of age to actually register on your forum AND store their date of birth as well for your requirements.
You can also add this plugin:
https://community.mybb.com/mods.php?acti...w&pid=1516
Quote:Require users to certify their age via a form check stored as a cookie; similar to Jcink's age verification process.
^ This one will simply require them to accept/verify they are of age to view the forum in the first place. A secondary measure similar to how alcoholic beverage sites work, requiring DOB before anything can be viewed.