I do think that the holders of most raw copies are part of a similar age group, i.e. "Boomers" born between 1946 and 1964 who built up their collections in the 60s, 70s, 80s, and 90s. About 90% of Boomers are still alive. It is reasonable to predict that that 90% figure will be dropping quite a bit over the next decade as the oldest Boomers enter their 80s.
I really don't know what the state of comic collecting will be 20 years from now. Most of the Boomers will be gone by then, and, from what I've seen, that's the generation that has been the most active in the hobby through the years and the most passionate. I know that there are younger collectors who continue to enter the hobby, but I don't think that they'll be able to replace the Boomers in terms of sheer numbers or in terms of dedication. It saddens me to dwell on it, actually.