Which IP version
We might have a list of domain names, but will that stop people using an IP address?
And could an IP-level block ever work with IPv4? An IPv6 address doesn't really feel human-usable, I am not sure I would want to read it out over a telephone, or listen to it and get it into a computer.
Proving age could be a problem too. I am old enough to have been spammed by the Green Card Lawyers, and old enough to remember the frauds that have surrounded proof-of-age systems, but how do I prove it this time?