I think it would be nice to have some kind of 'shelf-life' for old threads. Lets say anything over a year or so, and the thread should somehow no longer be available to be posted on. It would be a good way to clear out old threads. Just a thought.

Well there is no Quick Reply box on old threads, and AFAIK a warning banner is added to those threads when people do reply. There are potentially reasons for wanting to reply to old threads (but not usually applicable for sure...) so making it impossible would seem like an unlikely route to want to take. In line with so many angles you see in the behaviour of users not really able to use forums correctly, they seem to blunder on regardless of whatever you do. The number of people who "reply" using the "Report" button despite the large bold red writing on the submission page is nuts.

As Chris mentioned, we already completely disable the quick reply (which is by far the most common reply method at LQ) for old threads and make a note of a threads age on the reply page. We've already ruled out auto-closing threads, but if you have any specific additional suggestions, we're certainly open to feedback.

--jeremy