I think though the relevant point is that nobody “appeared” to struggle in previous generations . That doesn’t mean they didn’t , or that those conditions didn’t exist though. There is nothing new under the sun as the saying goes.
I went to a tiny rural primary in Ireland as well from the early 80’s to the 90’s & at least 2 of the 12 kids in my class have been diagnosed with autism or ADHD as adults (myself included). And after going through the diagnostic process with both my kids, I would suspect some type of neuro-divergence in at least one more when I look back.
Not sure what the UK was like, but in Ireland during the 80’s unless a child had profound autism there would have been no diagnosis- and for those children a special school (or little to no education) would have been the only option. So there would have been less awareness of the conditions among the general population.
There was also no resource hours or additional help for kids that struggled, and no understanding among teachers about any of the associated learning disabilities that sometimes go hand in hand with autism/adhd (dyslexia/dyscalculia and so on). I know a few kids that left school functionally illiterate or with nothing but the most basic numeracy skills due to nuro-diverse conditions. Back then they took “if it ain’t broke don’t fix it” approach. The criteria for diagnosis has expanded massively in the past few years.
And let’s not forget that back then, girls apparently didn’t have autism or ADHD. It’s only been in recent years that they have started to be diagnosed/recognised so that fact alone is going to mean that the numbers show a huge spike in recent years.
Finally Michael Healy Rae is apparently correlating the rise in autism with lack of vitamins, so he’s no better than Trump & Co.
There is no one definitive cause for autism, but in most cases there seems to be a genetic link (and I can say 100% there is in my family- my sister and I both have 2 kids, and they all have autism and are all absolutely perfect the way they are)