I have been asking the same questions. I have a blog that contains some hardcore pages and some that just discuss adult issues. I would like a WordPress plugin that allows you to show the age popup for only the pages that contain nudity or hardcore content. It seems that this paid for plugin does this, but I haven't tried it yet :
https://elfsight.com/age-verification-widget/wordpress/
I also want it to be geo-specific, so it can display the popup to visitors from the UK and some other prudish countries, but not others. I'm not sure if the above elfsight plugin can do that.
I am considering paying somebody to write me a WordPress age verification plugin that can both display it only on certain pages, and be geo-specific. Does anybody know a developer who could do that, and how much it would cost?