Grandfathers older than 50 linked to autism risk. My maternal grandfather had 12+ children; my mother was #12. So he must have been older, close to 50 anyway, although I don’t know his exact age when my mother was born. Moreover, I know nothing about my paternal side of the family. My twin brother is most likely an Aspie.
I don’t know that this explains Rob’s case though, since neither of his grandfathers were old: my father was 32, and my husband’s father in his 20’s, when we each were born.