I got a message the YouTube compression artifacts were affecting everything above 16,000 Hz.
I ran a test with real test tones and can still hear 17,000Hz the same as 8,000Hz, but frequencies above 18,000Hz were more difficult and I couldn't hear anything above 21,000.
I question their data on age versus hearing ability. I either I am the luckiest drummer on the planet (who also shot guns regularly often without protection until I was 23 years old), or their data is just wrong.