I'm not agreeing or disagreeing with the OP, or you, but the 1950's and '60s should be "mid-20th century", not "late". I don't know if there's a commonly accept

I'm not agreeing or disagreeing with the OP, or you, but the 1950's and '60s should be "mid-20th century", not "late". I don't know if there's a commonly accepted definition of "early", "middle" and "late" that does not involve waving hands.