When will we ever learn?

When you're under twenty one, or so, it can be really annoying to see older people dismissing your views as if you know nothing at all. And sometimes the oldsters who dismiss you can overlook something they need to know. Their rude disrespect or arrogant sense of superiority can blind them and cost them. But having said that, I'm old enough myself to see why it happens sometimes.
The same old things go around and come around.
I'm a nineteen fifties model. I was born in 1953, the same year the Korean War ended. I can remember newsreaders talking about President Eisenhower. And I can remember one of the catch cries from the time: "Ban the bomb." That was the anti nuclear activism of the day.
I can't recall the exact order or the times when the different politico-social fads went round, but in the sixties and seventies the Western world went through phases of concern about global crowding and famine, then pollution, especially in the very late sixties with acid rain. There was concern about heavy metal poisoning of soils, of water ways, all legitimate concerns, but the point is: these themes came and went, and then came again. There was even a global warming alarm sometime in the sixties. People were afraid the number of humans would generate so much body heat that they would raise the planet's temperature and it would start killing crops and causing starvation.
If you live long enough, you see the same things come and go and then come again. If it's the first time someone's heard it, they think it is new. They don't understand why older people are less impressed. To them (us!) it's a case of 'here we go again.'
I'm convinced the world will end, when Jesus Christ comes again. It will end when God decides the time has come. Nothing humans can do will stop that, nor should it if they only knew what was right. Nor will that day come any sooner than God decides, no matter how much humans think their behaviour changes things. So we have a finite span on this planet, no doubt; but it is rather vain for people to think it all depends on them.
How long before people get it?