Well, hagtech, you are of course correct -- and obviously so, even to those of us without mathematics backgrounds -- yet the matter may be even more complex.
Your answer apparently assumes that the percentage of people in the population who are audiogon members would remain constant even as new members join and older members die or otherwise no longer participate. But this may not be accurate -- it may be that as younger persons raised on video and ipods mature, fewer grow into audiophiles, while those of us who are older are more likely to become and remain interested in hifi. If this is correct, then the population of audiogon may in fact be aging. But a further hypothesis may complicate matters more -- that younger audiophiles are more likely to be computer-literate, thus skewing the percentage of audiophiles who might participate on a site like this toward a younger demographic less representative of audiophiles as a group.
I don't have access to the data -- and to me it's a matter of passing interest only. But the people in charge of this and other sites might actually care about the age of the audiogon demographic.
And in response to the question, I'm a lawyer, age 54.