If you dont want old threads laying around just delete them. Isnt there other things to worry about? Example if I have a strange rash on my backside, I would be worried. If a thread is 31 days old? Not so much.
I might be in the minority Pappers, but I know I find it annoying to see a thread over a year old get bumped with something to the effect of "Neat!" or "I gotta try this". Kinda feels to me like someone just wanted to go "postcount +1"