They're of similar construction, and it's categorically false that the 737 classic had a maximum 20 year lifespan or they're living on borrowed time after that.

They're of similar construction, and it's categorically false that the 737 classic had a maximum 20 year lifespan or they're living on borrowed time after that. They're routinely operated as cargo aircraft in the United States, just like many other older jet aircraft (for reasons of operating economics, not safety)