I'm not underaged, but I want to know: If a user who is underaged has founded a wiki, and fandom finds that user is underage, will that wiki be closed?
No, the wiki won't be closed because of that but the account of the user would get disabled anyway, it doesn't matter if it leaves the wiki without an admin. If the wiki has a wiki representative, the community can choose a new admin, or someone could adopt the wiki.
@Fandyllic If I was that user, I would also say that thinking someone would block me for no reason; COPPA does not allow users under 13 to share any private information for their safety but it's ok if they do not reveal any kind of private information and COPPA does not mean to go and find underaged users who have not revealed any personal information.