I'm a 73-year-old Canadian programmer with no formal education in computing. After completing a PhD in pure Mathematics, I started working the next day writing

I'm a 73-year-old Canadian programmer with no formal education in computing. After completing a PhD in pure Mathematics, I started working the next day writing scheduling algorithms in Fortran on an IBM 4341 (my supervisor played poker with the company President, so that helped). Although I picked up Fortran quickly, I had to study scheduling algorithms because my specialty was mathematical logic. Then I became a university Statistical consultant, but I knew nothing about that either (my boss wanted to learn logic). Five years later, when Prolog became a popular AI language, I quit my job and began writing expert systems as an independent. Prolog (PROgramming in LOGic) is based on the first-order predicate calculus, so my formal training was exactly what I needed to understand logic programming. After that I branched into databases, which I'm still doing as an independent. So, I didn't need to know anything about computing to become a programmer. But my domain knowledge (math) gave me a powerful tool to solve some computing problems.