"Hearing tests do NOT reveal all there is to know about hearing.
The sine wave testing they use is really tough to listen to.
In the 'real' world the upper frequencies can be noted even by people with hearing loss. They may be down lower in strength, but ARE still hearable."
Nothing reveals all there is to know, that's a pretty safe bet, but hearing test will most likely identify where certain limitations are, especially with older ears hearing high frequencies.
The good news is that most of what happens in music occurs in the range that even older ears are likely to still hear well.
Age almost acts as natures perfect low pass filter. I always found that most things that really annoyed me in home audio occurred at the highest frequencies I could hear when I was young.
When I was ~ 20 or so, I was able to hear quite well and "flat" out to 20khz, which is what most home audio is designed to cover well.
That's based on listening to test recordings (vinyl) at the time I had and still have that produced reference tones up to 20khz.
Now I am 54, and same tests detect little above 12khz or so.
But things still sound better than ever to me these days.
Its a scientific fact I am afraid that the ears sensors deteriorate with age, albeit to different extents case by case.
The good news is that our ears become better trained over time to do their job better, albeit within different limits/constraints.
Aging sucks though for the most part. I suppose the alternative is no better, but dunno and hope to not find out too soon! :-)