You can almost guess someone's age from that alone - they're more rare, but long domain names still appear that encode a city and a state, and you could just "grab" the first part when signing up.

Outside of the context of ccTLDs and city.state.gov etc, I struggle to think of examples 3LD+ domains where they are owned and operated by completely different concerns than the parent. If at some point you could just register your own mysite.state.gov domains willy nilly that's probably before my initial time online around 2000.

Another poster raised the point of hosting services which is valid. But at present outside of that example and the above I really can't think of an example where you have a link to entity.com and you have any significant cause to verify the identity beyond the 2LD.