Without headphones, I'll admit to not hearing much past 16kHz, with my headphones, not much past 17kHz. Years of live music in loud bands takes it's toll! Not to mention, at 54, it's about average, from what my audiologist tells me. But a FAR more important test is how much attenuation you get in the 2-6kHz range, where speech and much music's fundamentals exist. That's a far more important test, but hard to check without rigorous checking of your test gear.
To be honest, unless you set AND LEAVE your levels for this test at the same level, it's really a bullsh*t test. If you crank those high frequencies up enough, to be honest, with an MP3, you aren't really hearing the test tone but artifacts from the encoding process. Not to mention aliasing from your soundcard, etc.. Self administered tests like this don't really show much, I'm afraid. Want to REALLY know where your hearing is? Go see an audiologist (not a rep for a hearing aid company!)...
Of course, I'm sure that many of you realize that there isn't a single musical sound in those ranges, just the upper limit of some of the overtone harmonics. You might miss a hair of detail, but it's not really a true test of whether your hearing in general is any good. Most of what you listen to is a good two to three octaves below those test tones.
But, no doubt those who claim to hear up into the 20kHz+ range are feeling good about themselves...
But here's a more important question...
It's not whether you HEAR like a teenager - it's whether you PLAY like a teenager!
Or post here like one... That test has already been failed by some here, without them even being aware of it