Preventing replies to posts X days old?

[Ingenious]

Hi everyone, had a search for this but could not find anything. I might be searching for the wrong terms, I'm sure other forum owners have a problem with people replying to threads that are very old. The result is a very confusing mix of old and new posts.

Is there any way (or mod) where I can restrict certain usergroups (not admin usergroup) from replying to threads that have not had a post in X number of days?

For example, if a thread has no reply in 3 months or more, users cannot post a reply (thus enouraging them to have to start a new post)?

Or, I wondered if there was a simple hack that checks the date of the last post, and if > certain age, does not display the post reply button?