I would say it's reasonable time for Delta to phase out all aging fleets. We flew to Maui, Hawaii recently on L-1011 and it's like falling apart. I am not going to be sorry to see that plane being scrapped out however other L-1011 we returned back to LAX was better.
My wife and I flew 767-400 from LAX to SLC yesterday and it was impressive. Probably the nicest plane we ever flew. We flew 727 to MSP and it was nice, though. I am going to miss them.
By the way, I would like to hand my hat off to Delta for their outstanding service on our roundtrip from MSP to Maui. Everything gone perfect and timely without any delays or lost baggage.