Originally Posted by BetterRed
I think I've seen an 'Are You Sure' pop up appear on other VBulletin boards when Submitting a post to a thread that's older than 'nn days'. My suggestion for 'nn' would be 30 days.
If you're going to have a warning, I think it should be visible before you reach the stage of submitting the post. You need to be aware of it before you even begin composing the post. (But, on balance, I would favour keeping the thread open indefinitely.)