synkrotron - yes I agree about losing your high freq when you get older. I'm also a drummer so I've burned a lot of ear drum cells doing that! My wife says I have CHS disease! But when a song comes on, I'm always saying, that voice needs to be 2db higher, or that reverb is too long for my liking, or this or that.
I think it may be that I've learned, at least in music, to hear changes in other things that happen when you change EQ in the high freq range. For me, being a drummer, I listen to the hihats and can hear a change in them. Also, if I recall the test didn't have anything really high, seems like the highest was in the range you mentioned, 12k-14k.
I'm just stumped about the mp3s. I went from selecting the right answer in a few seconds to failing over and over on the mp3s! Obviously some change that I've not trained my brain to recognize. hahaha.. It's hell getting old!
gabo