Okay. Certain age: no, as long as you are thirteen, so can make an account, you could apply to be a discussion moderator. I don’t like to say my age, but I’m certainly a lot younger than most users.
Criteria: To be accepted as a moderator, you have to be a user with some experience, though that isn’t everything. Take Echo. He became a mod after only being on the wiki for, what, two months?
You have to have shown previous examples of good moderating (which I didn’t know when I first applied, hence I was not accepted). This could be on the Discussion Boards, threads or even article comments. If someone doesn’t understand or doesn’t follow the guidelines, you can nudge them in the right direction. I don’t say this enough, you don’t have to be a moderator to moderate. If they continue to break/not understand the guidelines, you can notify a moderator or admin who is better equipped to deal with the situation.
Finally, and this is perhaps the most obvious requirement, you have to be active. If you disappear for weeks at a time, and are inconsistent with your activity, admins will be less likely to accept your moderator request. However, if you moderate well, are friendly, and help people out, how active you are doesn’t matter (to a degree).
There are more requirements as well, ie trust, but I listed the main three.
What do you have to do to moderate?:
For this, I think it is best to quote the Avatar Wiki:Moderators page:
Moderators are members of the community who have a few additional abilities to help administrators maintain the wiki. They are able to remove and restore replies that are not their own on message walls, forum threads, and Discussions under the conditions established by our discussion policy and Discussions guidelines. They also have the ability to close threads and Discussions posts.
On top of this, Discussion Moderators can now regulate article comments (which were recently added back to the wiki), though the page hasn’t been updated yet.
I hope this helps, and if you have any other questions feel free to ask them or check on the Moderators page.