"Old Internet" doesn't have a very defined meaning, but I think it has more to do with design and functionality than a hard date. While I don't think relevance matters, 4chan is much more relevant than you think. Having a niche is part of the old Internet. Websites used to be niche, but deep, instead of websites like Wikipedia, which are broad and shallow (compare the Castlevania dungeon [0] to the Wikipedia article for Castlevania, for example). Then compare 4chan's limited number of boards with reddit's endless subs. 4chan's design is early web 2.0, doesn't require you create an account, allows (pseudo) anonymous posting, content is mostly unfiltered, unmonetized, free & thought of as ephemeral, etc.

0 - https://castlevaniadungeon.net/dungeon.html

22 years is old. Nobody knows what geocities is, it has no relevance. It’s like talking about brands of telegraph wire.

Geocities was going strong in the late 90's too! My first homepage was hosted there on Tokyo Towers.

It is not very niche at all. 4chan served a gigantic volume of traffic.

Side note: When you google "Geocities" the results are in comic sans

Web 2.0 and before is now considered the old internet.