My Hi-Tensile steel '75 Fuji is still going strong after 40+ years. I have absolutely no reason to think it would not last another 40.
__________________
'75 Fuji S-10S bought new, 52k+ miles and still going!
'84 Univega Gran Tourismo
'84 Univega Viva Sport
'86 Miyata 710
'90 Schwinn Woodlands
Unknown brand MTB of questionable lineage aka 'Mutt Trail Bike'
Plus or minus a few others from time-to-time