Thanks for all your suggestions. Here's a few observations.
The graph that Greg Bosley posted is very interesting, as I noticed clearly that dip and rise again between 4 and 8kHz.
The drop-off in my higher frequency hearing probably explains why I have gravitated towards bassier music as I've aged, especially EDM and drum'n'bass, something I have surprised myself with. And I now hate those heavy metal singers who screech in falsetto. Love the shredders though. Viva Stevie Vai!
I've always enjoyed my music LOUD; maybe that's caused it. Let this be a warning to you youngsters :o)
Blues harp is my main instrument, and I've started playing low-tuned harmonicas rather than standard ones.
I'll just have to live with it and get a second opinion (and 3rd and 4th) for any mixes.
I'm sure I can't be the oldest here. Any other "mature musos"?