Ok......then listen..........It all pretty much changed after industry deregulation 1978 deregulation. Prior to that, as you say, age 30 for the Majors was pretty much the cut off and physical standards were very high. You pretty much had a job for life if you got hired at a Major back then, with a couple exceptions. There were furloughs every so often but you always came back. Seat progression was very slow........many spent 10 years as an Engineer. 15 to 20 year Capt upgrades were not unheard of. That all changed with the mega expansion and many start ups post deregulation.