When I went through school in the 1950s, algebra was a HS freshman subject that most took. After graduating from college, I taught HS math (algebra and pre-calculus) and computer programming (via GE/Dartmouth Timesharing) for 5 years ending in 1970. For that period of time, algebra was still a HS freshman subject.
Having said all this, I actually learned algebra in 8th grade; however, it wasn’t taught. I got a hold of some of my dads’s books and taught myself.