Jazz certainly has a very elderly audience. Many (like myself) will be survivors of the jazz boom of the late 50s and early 60s (the Blue Note era) when they will have been in their late teens or early twenties. My late friend John Shelton (JohnS of this forum) who ran the Portsmouth Jazz Society used to say that as aficionados passed on or grew too infirm to attend gigs they were never replaced by anyone younger and so the numbers of listeners was in steady decline. Some venues have younger audiences, though, but they are still not as young as their twenties, the few exceptions being those who are studying, or are the products of studying, jazz courses. I'm aware, though, that this picture which is true for this part of the world is not universal. Whenever I look on YouTube at what was on a few hours earlier at Smalls Jazz Club in New York City, I'm struck - and heartened - by the youthfulness of the audience in which twentysomethings are the norm and old guys like me are never seen - except sometimes on the stand.