I've seen lots of blind locking of old threads with the justification that "they're old". This is simply nonsensical.
Case and point, this thread. The instructions are applicable today, useful to people, and there is valuable discussion to be had on the topic. The fact that the thread was "started" some 21 months ago is not important. The thread contains valuable information and contains an unresolved problem. If somebody can find a resolution to that issue, it makes sense to add it to the existing thread rather than separating the content into two threads.
I'm not sure how such forum guidelines are designed, agreed upon, or implemented, but this one simply doesn't make sense, and ought, for the good of the forums as a whole, to be revoked.
</my tuppence worth>