@SmoothBrainDev: When in doubt, I would stick to the advice from Dark Dimension, as they are more experienced with using itch.io, interacting with its community + moderators, and actually distributing games though this platform - and presumably through other platforms as well. :)
That being said, as far as I am aware itch.io offers no kind of scale at this point in time. There is a collection of tags that interact with the “Show content marked as adult in search & browse”-flag from our user settings. And that’s it.
Hypothetically speaking: If I was a legal guardian, I would hope that my beloved underage offspring doesn’t see anything that I personally would consider “adult content” when I leave that flag unmarked. But if it was important enough for me that they aren’t shown such things, I would (have to) do the responsible thing and supervise when they browse on itch - or at least have them ask me if it’s okay for them to download games before downloading something. And if junior were to ask me if it was okay for them to download Bloody Gore and Firm Bananas (Part 7), I would write a somewhat impolite letter to the dev and/or itch as the platform holder.
Or I could say “You’re old enough. Just don’t install something that would scare my better half.” and waive my right to complain. At least that’s how I understand parenting.
I hope this helps.