Somebody who says "good ear" can be talking about how well trained a listener is rather than the physical characteristics of their ear, similarly to how when somebody says "good eye" when you spot a bug in their code they're probably not actually implying your vision is extra sharp.

I’ve lost a noticeable bit of hearing, but my ability to discern different instruments is much greater than it used to be. I think practice more than offsets hearing loss up to a limit.

Yes. You still see the claim that humans can hear 20Hz-20000Hz. Well, no. We had lab equipment at school and we regularly listened to signals from test equipment - IIRC I could hear up to about 17kHz when I was 16 or 17 (when I could still hear the (European) 15625 whine from TVs). A couple of guys could hear almost up to 20kHz.

All of that was gone when we arrived in our twenties. I couldn't hear the TV anymore (younger people: That applied to analog CRT TVs back in the neolithic). I was tested in the military when I was 22. They didn't even bother testing anyone up to more than maybe 14kHz - intense volume would anyway be needed to hear that.

I can't imagine even very careful people will be able to hear a particularly wide audio range when they're 50+, not even people who walk around with ear plugs all the time for protection (some audio engineers do).