Board Thread:General Discussion/@comment-4343163-20130607184538/@comment-3030984-20130608105149

Per the Terms of Use:
 * "You agree not to use the Service to...Solicit personal information from any user under the age of 18"

As you don't know the age of any given user, you have to assume that they may be under 18, and hence you cannot ask a user for their age without violating this rule.

More importantly:

It is not the responsibility of local admins and chatmods to determine who or who isn't underage. Wikia, as a company, enforce a minimum age of 13 so that the site complies with COPPA legislation. Hence, it is the Staff of Wikia who hold responsibility for enforcing this. While Staff welcome reports via, admins are not asked nor encouraged to ban users locally based on age.