Marc,

Short of just allowing a thread to scroll off the forum (which I know you don't do, as you have enough storage for this not to be necessary) I don't think you'll find forum software that will sort the threads and stop ones that are dormant.

At least, if you do, I would be very interested to know, as I help out in a couple of forums on the 'net where that would be a very useful function and I've spent hours over the years trying to find it.

Anyway, IMHO, in this hobby of ours, things stay relevant for years; decades even!

-David C.