I covered them in high school, but in isolation. I think it'd have to be a dedicated high school program explicitly built to cover differential equations and tie them back to physics and then also get far enough into EM for that to be the way you can teach about radios. Not even remotely all high school students could handle that and I think even in an accelerated program you'd have to consciously be sacrificing something else to get there, e.g., organic chemistry or something. There's only so much time.

I mean, even in college, the physics I took that did EM with full, undiluted multivariable calculus was considered the accelerated/advanced track. "Normal" EM worked with a lot less math.

I'm sure the 1950s kids were indeed learning handwaving approximations. That's not a criticism. You can get a long way on good handwaving approximations.