I see a problem with the assumption that old threads have no current relevance or value. For example, there's a thread on parking that I started 11 years ago that keeps popping up in the Disability forum because the info is still relevant and the links accurate. Periodically someone asks a new question and updates, if needed, are made. That thread contains valuable info for a specialized situation, and deleting it would take away info collected by that community that is hard to find elsewhere.

If a resurrected thread is no longer accurate or useful, lock it. But don't assume every old thread is worthless.