What I'm suggesting for different service levels is simply to map a specified access / age-verification level to a specific network access point. This is better suited to IPv6 which has a much larger address space than IPv4, and often allocates a range of addresses rather than a single IP, though NAT or IP shenanigans might be possible for the latter as well.
The point is to put the heavy lifting of age validation at a level at which who is getting the service has already been vouched through service account provisioning.
It's less that there is something unreasonable sounding about it and more that there's almost nothing that sounds reasonable about it. It's like you suggested that instead of setting speed limits, we directly tie the maximum speed of a car to how far the driver's seat is from the steering wheel.
What I'm suggesting for different service levels is simply to map a specified access / age-verification level to a specific network access point. This is better suited to IPv6 which has a much larger address space than IPv4, and often allocates a range of addresses rather than a single IP, though NAT or IP shenanigans might be possible for the latter as well.
The point is to put the heavy lifting of age validation at a level at which who is getting the service has already been vouched through service account provisioning.