Of course I am no lawyer. Not even an US citicen.
From my understanding, influenced by some european laws no less, if a company claims they do this and that in their tos and do not, a competitor could demand action from the law. Because they gain unfair advantage. But the hurt party would be the competitor. And strictly speaking, only if what they say in the tos is to be enforced. Like real legal stuff. Or if it can be construed as false adverstising. Stuff like claiming to be environment friendly and lying about it. It might be entirely different in the US. But since itch is not acting against you, how would consumer protection protect you from itch...
I see two points that might be relevant here. I did not study the tos too deeply. But first, I did not stumple upon any promise that they obligate themselves to enforce their tos. It is a contract setting up rules between the user and itch. Not between the user and other users. They set the rules how they say they might act, if you break rules. This is important because you buy stuff for money on itch. And you can earn money there. If money is involved, rules become very important for some reason. Also for people whining about their banned account, so they can be directed at the tos, what they did wrong and don't go running to consumer protection.
The second point is, that this age restriction is worded non strict. So this could imply, that they might refuse payments to and from an <13yo account holder, but otherwise keep a blind eye, as long as the account does not make age related problems. Like buying 18+ games. Or selling games without parental consent (wich is impossible to get before 13 anyways).
And I feel you with the easier said than done. I had my share of places I left because of strife before I got ... more patient.
But I disagree that itch is social media. They share some aspects and confuse some people with it. It is more classical forums. And the following stuff is catered to devs publishing stuff. You do not see my posts, if you would follow me - as you would on any real social media.