If you're like me, an admitted AvGeek, you always look at the tail number of the plane you're flying. And when boarding, you look inside the open front entry door for the small metal plate that reveals when it was built.

In recent months, I've been flying on some pretty old aircraft. And who flies the oldest plane? That would be Delta. Tail Number N649DL belongs to a Boeing 757 that rolled off the assembly line back in 1989 — about 37 years ago. But there are other old-timers in the Delta fleet.

The most recent numbers: Delta is flying 38 active 767-300ER models averaging 28 years old, and 30 other 767-400 models averaging more than 24 years old. And Delta won't be retiring the 767-300's before 2030. United flies 53 767's averaging more than 28 years in service.