I also stand against the implementation of a generic age rating system, and would be more happy with some kind of selective "in a category I may dislike" type of warnings system.
And of course there is a huge need for adding some way for users to personally blacklist or ignore games based on tags. At least I can say with confidence, that the "Adult" and "NSFW" section of the site is unpleasant to browse through without any options on content filtering.
My main point is that, people can be adults, with very different tastes in whatever. So a generic "you are 18+ so you are okay with anything" type of system wouldn't work well, and wouldn't improve itch website's current state in any way.
If itch decides to move to a generic, age-based rating system, then at least there should be a separate "For Adults Only" category besides the simple "18+" category, as it's possible to find things on itch with rather odd, uncommon, or extreme content, which surely doesn't pop-up in "simple" "18+" computer games. And here comes in the problem about defining what is allowed in the terms of service and the sensitive matter of artistic freedom and censorship, which I think that anyway can not be enforced without a sophisticated manually supervised curation system, which would at least be able to correctly recognize and tag all games on itch.
By the way, why is it not allowed for users to add tags to games? It would make it a lot more easier to search through the whole selection of games on itch, and more probable to find what people are looking for instead of totally random stuff, even without implementing a tag blacklist system.