From
isomorphisms, these pages are nice because they provide a sweep with a voiceover telling you what frequency is playing, and you merely need to hover the mouse over the little orange dot to get it to start playing. I recommend doing this with headphones at fairly high volume (especially headphones that are rated at least at 20Hz to 20kHz).
Low Frequency test(this is more a test of your equipment - I don't know that people normally lose their ability to hear down to nearly 20 Hz)
High Frequency test I'm 31 and I can still hear to nearly 18 kHz, go me, I guess? Hopefully I can get this to last, if I want to make a career out of audio editing... (because it's useful to be able to detect when there's a high pitched hiss that needs to be dealt with).
(I start hearing the sound ramp in right after he says "18 K", but on a
different site that plays steady tones, I'm able to clearly hear the 17k tone but not the 18k one at all).
But practically speaking, given the logarithmic way that frequency relates to pitch perception, losing a few thousand hertz off the top doesn't amount to much. For example, in terms of musical notes, being unable to hear above 14 kHz amounts to losing only six half-steps (half an octave) off the top, out of a total of 10 octaves perceivable at birth! So getting older, losing the top 20th of one's perceivable pitches... no big deal. Check out this cool
interval calculator (100 cents equals one half-step).