Just the Facts:
Average age of NWA fleet 18.5
Average age of DAL fleet 13.8
http://www.airsafe.com/events/airlines/fleetage.htm
That link is not accurate it's counting 111 DC-9s. I believe there's quite a few less than 100 flying now and only 6x at the end of the year so that fleet age has to be way off.
Who cares anyway?