I didn’t feel like spending the morning looking up statistics about a/c, but the last time I did (maybe a year or so ago), I think I remember that a/c crossed the 50% (of homes) threshold during the 60’s. In other words, it was still considered a luxury during that period.
I had a great childood in the '60s. Grew up middle class in my parents first brand new house. It did not have a/c, and every home on the block came with a clothesline in the backyard.