The trucking industry has a very long tail when it comes to equipment. Big trucking companies (100 plus trucks) generally replace their equipment every 3 to 5 years. Smaller companies (10 to 100 trucks) often buy a mix of new and used equipment with an average age somewhere in the 5 to 10 year old range. Then you have the majority of the trucking industry who buy whatever makes financial sense to them at that moment in time and then run it till they can no longer get parts or they hang up the keys. The latter being more common.
As I was writing this a cab over Kenworth drove by the dock I’m currently parked at. They haven’t been made since the late 80’s, I think. Once the tech is available, then a 10 to 20 year time frame makes sense and will see some 90% to 98% of the old trucks replaced.
You might like this YouTube channel:
https://youtube.com/@edisonmotors?si=_O5hmnkl56oarlx6
Canadian trucker with a mindset like your friends dad, but also is building trucks that is in my opinion the way forward for the trucking industry. Got to bounce, load to move.