Hiya! I really love the content tags idea that lots of people have been bringing up (especially the added suggested tags for seizure and trigger warnings!). And I believe that tagging your content should be a mandatory step for devs when creating a game page, not an option in a sub-menu somewhere--that way there's less chance of mistakes being made. My favorite way to implement this which was mentioned a couple times were some simple buttons that the devs click on with the option to specify a little more about each one.
I also think that the categorization of games into the broader three groups - Everyone, Mature Audiences, and Adults--is much, much better than specific age ranges. But I don't know if that should be determined by the devs or the site--maybe, depending on what developers select in their content tags, itch.io "recommends" a category, but creators can override it?
Lastly, my biggest concern as a creator is what to do if, for some horrible reason, a group uses the flagging system for miscategorizing to try and harrass a developer or try to get their game taken down. I'm not as worried on such a progressive and considerate place like itch.io, but I've seen it used before on creators on other platforms, so, y'know, it's on my mind!