[Roseval]

You are on the right track.
 
Age related hearing loss happens to all of us.
Believe or not the older we get the more it will manifest itself
You can easily test it yourself e.g. http://newt.phys.unsw.edu.au/jw/hearing.html
 
My hearing is capped at 13 kHz
Basically I have told you now that I'm approaching my mid 60's
 
An A is 440 Hz.
​Indeed all instruments playing a A sounds the same as far as this fundamental is concerned
They also produce the harmonics, that is where they differ
You can imagine that a you can easily hear the 2/3/4/ harmonic before any of them hits the upper limit of your hearing.
​You have the almost full coloration produced by most acoustics instruments. 
 
Pragmatically spoken: I do hear a profound difference between a HD600 and a HD800 or a Ety4P

 

[dprimary]

   
Anyone know of any surveys done to quantify this? I haven't seen anything that shows a top-end by age, and the numbers I have seen from health surveys focus on losses at much lower frequencies.

 
 
 
 
Here is two papers starting with the first known one
 
Francis Galton was researching it in back in 1883 and had whistles made that went to 84k page 26 and page 252 he writes about them. Not much in details of what he found.
http://www.mugu.com/galton/books/human-faculty/text/galton-1883-human-faculty-v4.pdf
 
The Evolution of Human Hearing
Bruce Masterton1, Henry Heffner1 and Richard Ravizza1 J. Acoust. Soc. Am. 45, 966 (1969)
 
Measured the upper limit to be 18KHz with threshold of audibility being 80dBSPL vs 0dBSPL for 4kHz where we are most sensitive.
 
There was tons of research done in the 50's you could spend months going through references back over 100 years.

 

[Wiljen]

did some informal testing and without calibrated equipment I know the exact numbers mean nothing but the patterns were revealing all the same.  My wife and I both lost the ability to hear the tone between 12 and 13k while my 17 year old daughter could hear well into the 16k range.
 
By using the volume adjustment to normalize the level of the tones I was able to find a dip in the lower mids for myself that neither my daughter or my wife shared.  I don't know if that is indicative of some form of loss or just person to person difference as it was only a few Db difference.  
 
The other interesting takeaway was the frequency at which each of us felt tones got shrill or piercing, I was the lowest, then my wife almost 2k higher then my daughter about another k higher yet.   With this small a sample size and the complete lack of any scientific method I know it means little but I cant help but think this kind of difference from one of us to the next defines why some find a paticular IEM or headphone sibilant and other don't or why that mid boost is pleasant to some and annoying to others.
 
P.S. if you do these tests, put the dog out first it thoroughly annoys labs and ridgebacks.

 

[limpidglitch]

If you look at this graph that I posted earlier you'll see that there isn't just large variation between age groups, but also within them, especially when you look at the band between, say 4 and 16kHz.
I wouldn't worry much about a few peak and troughs, we've all got them, just at slightly different places. Much of the reason for this is that the anatomy of our ears and ear canals are slightly different, making resonant peaks and nulls move around.
 

 

[fjrabon]

   
For many instruments even 12k hearing gets you an awful lot of overtones, so I don't think you'll be confusing an oboe with a soprano any time soon unless you have really pathological hearing loss. I'm sure many older people can still tell a short high note apart on, say, a piccolo versus a piano. I wouldn't worry so much about it.

yeah, this is one of those things audiophiles are mostly clueless about.  I hear somebody once say that they "could hear less string attack on the guitar" due to a 14kHz dip.  The highest note on any guitar is 1320 Hz.  For a guitar anything over about 8kHz is completely unnecessary.  Most guitars are low pass cut at 8-10kHz in studio recordings anyway.  Same for most instruments other than cymbals.  You won't "misshear the tonality" of an instrument unless you have hearing damage extending into the sub 10kHz range.  About all you lose above 10k is cymbals sound less "airy"  With hearing loss above 10kHz you may lose some spacial cues, which can cause a loss of soundstage depth.  Really the only thing our brain uses the spectrum above 10k for is to judge the distance of sounds.  

 

[Toom]

I have scientifically discovered that a glass of single malt makes music sound better.

 

[Wiljen]

I have scientifically discovered that a glass of single malt makes music sound better.

It does indeed, the funny thing is, if you continue with too many glasses of single malt, at some point you either cease to hear the music altogether or start hearing music where none exists. 
I find that a single glass of something like Royal Salute along with a good Cohiba or Montecristo and a favorite recording can turn a mundane day into a really good evening though.