If you ran a library, would you throw away books that hadn't been checked out in five years?
That's not really a valid comparison. Books have much more long-term value (and some genres more than others) than posts on an online messageboard. As much as I love this place, it's just not in the same category as a good library.
Again - the policy is to not revive dead threads and double that for ones that are so ancient. Unless there is a very compelling reason to use an old thread, don't do it.