I'm now 42. Bought my '12 as a turning 40, midlife whatever, birthday present to myself.
I would say almost for certain the average age is 40's. I hardly ever see other people on 14's around here on the street (Ann Arbor, MI); and when I do its at the drag strip. Those guys are usually 30's to 40's. Most of the guys I ride with -my age, or slightly younger are mostly on 1Kcc bikes. a couple gsxr's, couple R1's, a zx10, Ducati 1098s, and a couple FZ1's.
As for getting older, and switching to a cruiser, Harley, or whatever; I just have no desire to own one of those. In another ten, fifteen years I might switch to a C14 or a bike similar to that. or maybe not.
If I get to a point where I have to have something more comfortable, I love the idea of having a big motor naked bike too. Right now, if I had to pick one it might be the BMW S1000r. I am dying to ride something with active suspension like that. Seeing as I'll never ride the all mighty HP4. I like the Tuono v4r also.
In the short term future, I might end up with a second bike for longer rides anyway; but will likely be a first gen FZ1. They can be had cheap enough.
But a Harley? probably never. If they made something with enough go, and the price was right; I could maybe change my tune. Don't see that happening. factory supercharged vrod? I'd buy a Ducati Diavel instead.