Being underage is not a good thing. You will get blocked on some wikis of Wikia and - if there are proofs which are sent to staff - even be disabled for all wikis on Wikia. If you are under thirteen years old, you are underaged.
Why Underage is bad
The kids don't know better, Along with the fact that Many times, Underage users can be common on Some Wikis (i.e. ESB for Example) It also Violates COPPA (Children's Online Protection Act), as it is against the law for anyone under the age of 13 to have accounts on wikia or any other kind of social media.