Would it be possible to make it so the DOB userfield is only available to admin and not mods / only available with a button click (the way email and IP are handled in core), or would something like that require a plugin rather than a theme component?
That is outside of the scope for this theme component (and it would indeed require a plugin).
The only thing it does is add a validation on an already existing user field, and as a consequence it will prevent account creation / storing the associated data for minors. It does not manipulate the user field in any way.
Richard i want to say this is really helpful something i have been wanting for my forum for some time now! Despite the user’s being able to get around it do you think if a user puts a birthday not old enough then changes it to use the forum admins are notified oh user first put X date then changed it so staff can be aware?
Although it is an interesting discussion, please limit this topic to the age check theme component itself.
This component merely adds a check to an existing user field. It does not introduce potential privacy issues - on the contrary: it can prevent minors from signing up.