User blog comment:AllHailPeterTSW/Why do you have to be 13+ to be on wikia?/@comment-26437440-20160925002616

"In order to use certain portions of this Service, you will need to first register for membership in the Service. You are prohibited from registering for membership in the Service where prohibited by law. In addition, the Service is intended solely for users who are thirteen (13) years of age or older. Any registration by anyone under 13 is unauthorized, unlicensed and in violation of this Agreement. By registering for the Service Site, you represent and warrant that you are 13 or older and that you agree to and to abide by all of the terms and conditions of this Agreement" - Terms of Use

Also (COPPA).

It doesn't matter how well behaved you are, even if you make plenty of great edits Wikia will still block your account if you're under 13.