IBM 1401, as a high school junior in 1964. The 360 was just a set of posters then. I needed to do some number-crunching for my science project, and IBM gave me time on weekends.
I started out writing the program in assembler, until someone came by, wondered why I was despondent, and introduced me to Fortran.
The school felt there were no really worthy projects to send on to the big-time Metro Detroit Science Fair, but thought mine was the best of a mediocre bunch. It won first prize in the math division, and might have won best-in-show, except I was on the junior class trip, and couldn't be present for the judging.