I graduated HS in 1973. Oral sex was popular then. It was probably popular when the first caveman took the first cavewoman on their first date....
I wonder if the fact that I went to a very small, rural high school made a difference. I literally knew every single girl in the high school (every single kid for that matter) by name. I'm not saying that nobody had ever heard of oral sex, but I was part of some pretty frank discussions on sex, and that never was spoken about. Don't know if it was different in the larger schools in the bigger cities where they were more "sophisticated" about such things.