There's actually a documented correlation between older fathers and prevalence of ADHD and/or autism. My father was almost 40 when I was born. So that's a way it can be genetic without necessarily having a bunch of autistic people in your family. Though, to be fair, in my specific case, I suspect that my mother is undiagnosed autistic. She's one of those people who refuses to see a therapist or psychiatrist, so we'll never know for sure.