I totally missed this thread, sorry. x3
Essyrn reigns as the oldest permanent settlement. Serendipity is the oldest of the Three Kingdoms. Connlaoth comes in second and Adela would be third. La'maari and Zantaric are the youngest of the settlements.
Some settlements in Yoreiq are quite old, dating back to about the time the first settlers began populating what would become Serendipity.
People (humans and otherwise) have inhabited the Niahi Woods and Kishahn Jungle longer than any other region, but there are no permanent settlements in those places. That is, you'd mostly find small villages and communities that form, last for as long as they can, then break up and move on.
Aaaaand Thanatos I don't know about. x3