I stumbled upon an old question with an equaly old answer, which is totally useless (or just not an answer). Should I still flag this answer, with a comment for moderation? Is there a time limit, to how far back answers/questions should be flagged?
Yep. People coming in from Google won't initially know that the posts are old, and may not care even if they notice. They will care about quality, though. Fight cruft everywhere!