What's the second oldest torrent? That's probably a better measure of the network health, because it doesn't get attention from articles about the oldest active torrent.
Though I don't know if it is a good indicator. Even though, at the time, BakaBT was semi-private and not private, lessening the incentives to seed as one could download without limit by logging out, it still has a system that rewards seeding torrents with no/few seders.
according to the thread here: https://news.ycombinator.com/item?id=10962253 an article about the then believed to be oldest torrent, turned out to be a few months less old than this one, so we need to look for the third oldest now to get a good answer.
on piratebay i found a torrent from 2008 that still works.