I'm thinking about closing the question Are air purifyers and ionizers effective? for being off topic, even though it's an old question. Is there any reason not to?
If a question is off topic it's off topic regardless of it's age.
We can't be expected to review every question as it gets posted and off topic questions will slip through occasionally. In this case when an old, off topic question comes to your attention then do one of the following (depending on your reputation):
- If you have less than 3,000 reputation flag it for moderator attention.
- If you have more than 3,000 reputation vote to close. You might want to consider flagging as well (using the "other" option) if the question has low views and you don't think it will get the views necessary to get closed by 5 community members.
- If you are a moderator then just close it :)