Make a rule on joking about being underage

I recently reported a user for joking about being underage, but now they are saying, since its not in the ToS it is a false ban. I have had enough. Just make a rule on the ToS to not joke about being underage. Please. Source (contains swearing): https://amp.reddit.com/r/discordapp/comments/cm4787/psa_dont_joke_about_being_underage_on_discord/