As far as I can remember, we never got the "you need a jock" speech in PE. My vague recollection (this being between 42-46 years ago the memory is kind iffy) is that most of us didn't wear one. We did have to take showers in 7th grade ( I avoided it as much as possible being a fat non-athletic kid), so I would have seen them then. Showers for some reason weren't quite as mandatory in 8th and 9th (still at the same junior high as 7th grade). And my last year to take PE was in 10th grade in high school. I never remember taking a shower there. But even without taking showers, we still had to "suit up," in our gym uniforms, so I probably would have seen if a lot of us where wearing them. Possibly in schools with swimming pools, a lot more of the boys would wear them.
My uncle is one of the Greatest Generation. He turned 93 in August (You'd never know he was 93. You'd probably think he was in his 70's. He's as sharp as a tack. Only in the last year or so has he slowed down slightly.) He tells me they swam nekkid as a jaybird (my words) at the YMCA except on Family Night.
I came across this little gem on the internet when looking up the subject just now-
"In 1885, the Brooklyn YMCA opened America's first recreational indoor pool and required men to swim nude. Wool swimsuits were potential traps for disease and bacteria, and fibers clogged the pool'ssimple filtration system. ... After pools installed more advanced filtration systems, swimming nude became redundant.Apr 26, 2017
Medium › dose › a-brief-humili...
A Brief, Humiliating History Of Swimming In Gym Class - Medium"
And of course we've talked on here before how millennials and possibly, gen-xers, are even more body shy than we boomers were.
Gman