As far as I was aware, there isn't one "cause" of autism. It's not yet fully understood and I don't think it's simple.
There is a genetic component - but some seem to have taken this to mean that if a child is autistic, one or both of the parents "must" be too. Yes, maybe many are - but also a lot won't be, and I don't mean those unaware, or in denial.
It's something of a personal irritation - I have an autistic DD and shortly after diagnosis we signed up for some local family SN support, thinking they'd suggest new strategies and ways to help and support her. The support worker spent more time trying to find out of DH or I were autistic (neither of us display any of the traits, both well-known or wider - and yes, we've read into it - both score v low on initial "screening" questionnaires, though there are some traits in wider family), than actually suggesting anything that could help us or her. How does late Uncle So-and-So having traits, none of which were the same as hers, help her and us now? We had few strategies suggested, little advice. Other than "maybe she doesn't want friends" (she does). I've also noticed a clear shift in the way professionals address us, more patronising almost. Which isn't appropriate even if we were autistic.
Don't even get me started on "x is rude = autistic"
"y is a bit quiet = autistic" "z has a quirky niche hobby = autistic"
"w is blunt and uncompromising = autistic" - it's not a byword for other people's at-times unfavourable character traits.
And a couple of minor "traits" can often be just that - traits. Like people who are tidy claiming to be "OCD" - it's seemingly harmless, but armchair diagnoses and glib remarks can often minimise the real struggles people go through.
There are well-documented health risks associated with later parenthood, and increased likelihood of many other conditions, not just autism, but most older parents choose to take on those risks in the knowledge that things will mostly be OK, and age isn't the only factor.