Every now and again there's a purge on the forums where they go through and delete old threads deemed not necessary to keep.
But there's no automatic deletion age set I believe.
Okay here's the low down then.
Usually only reply to something that is recent, as bringing up old stuff tends to make the page a bit confusing as to what people are currently discussing or need replies to. It's not an "official rule" exactly. But its a good habit to follow.
I don't mind if you...