My uncle, from the time he was a little boy, liked nothing more than farming and gardening. He has one friend and they talk exclusively about growing stuff. He had to be forced to finish high school because all he wanted to do was wrench on a tractor. He barely talks unless it's farming related.

He apparently takes after other men in the family, always one or two per generation, who were pretty much mute except when it came to their special interest. And they were 100% focused on their special interest.

Back in the day, it was "Uncle Bob just has those family genes. We get one of them every once in a while. He sure is a helluva good farmer." Today he would be diagnosed with autism.