This question really goes to the heart of this whole site. There is an oft repeated suspicion of composite and bonded frames, and a bent towards old skool steel. Fair enough. I don't think it is quite as cut and dried as some make out, but generally we are all leaning on our own experience. I would happily hammer an 'old' carbon frame that passes a visual inspection; if I believe it was lightly used. I would think that a better bet than heading down a mountain on an out and out downhill rig I know was used in anger. Still a bet though. That 'light use' may have been outside its limitations; vastly overforked or sat in the wrong place for its years, until I pick up the frame on its own.
The way I see it is I am a heavy older fella; and I don't generally have time or space to cosset a carbon bike for daily use. Day to day bikes here are thrown in vehicles, or stacked up and moved around with no attention paid to fragility. So in my use case scenario, old steel bikes make sense. I do have a bonded bike, which will be looked at very carefully before use. I also have several carbon bikes, which shall be sold. Just kidding, I will keep them from sunlight and proximity to anything lest they explode.
Aluminium is an odd one. I don't feel worried on them, but I know thirty years plus is a long time to amass lots of microfractures. Especially if that lightweight Klein came from an actual rider, who used it as intended. Unlikely I know. Then it is a case of using it lightly.
I think we all, to some extent, think the other way when it comes to longevity. Comes with the territory.