I'm kinda surprised that the rightsholders don't try to push the accountability onto the ISPs. The ISPs are giving the individuals their licence plates (IP Addresses) so are in a good spot to say this IP is allowed to access X content. For devices being a NAT then the local router can provide that information to the ISP to forward to the service.
There's already Australian High Court precedent establishing that Australian ISP's are blind providers of data with no obligation to spy on their users for the benefit of third parties wanting user intel to connect the dots. That was WRT torrenting, but it's a case that'd serve as a foundation for any push back in other related claims. * https://en.wikipedia.org/wiki/Roadshow_Films_Pty_Ltd_v_iiNet... This case is imp…
The rightsholder would look at the connecting IP and then contact the owner of that IP for if that IP was allowed to view age-restricted content.