I have finally implemented one of the long-requested features, to stop new users answering old questions. Editors and Mods can use this feature.
If a user under 200 rep answers a question more than a month old, the post will get flagged for moderation. You can see them on the Admin > Moderate link.
If an answer adds more useful information or corrects an existing answer, approve it.
If an answer adds nothing, repeats what's already said, or is generally incomprehensible, reject it.
Currently it is set for all questions, including moveset questions. For those, only reject it if the moveset is really terrible. If it's average then let it through and others can vote on it as usual.
Also, if anyone has ideas for any other posts that should be automatically flagged, let me know!