In the recent races I've entered, the men's 50+ entry list is about the same or slightly larger than the men's under-50 entry list. For women, the 40+ entry list is about double the number on the under-40 list. So . . . for races in Kansas, Oklahoma, and Tennessee, gravel seems to be almost geezer-centric.
I don't know if this means anything -- it might just be coincidence -- but I see the same (aging) demographics in the triathlons that I enter,