Interesting, thanks for the replies. Must just be the area I ride in then here and LA, Pasadena, etc. I do of course understand that "riding gravel" has been around as long as there have been bikes, and cross has been around for ages. But as I say, I'm one of the very few guys I see on a rigid drop bar bike on the dirt when I go out who has an AARP card
Most appear to be in their 30's,
maybe 40's.
Could also have more to do with my region. I was out the other day, coming back down to a trailhead and chatted with a geezer my age on a full sus MTB coming up, and he was poking fun at me for being one of those "tough guys" riding a bike like that off-road (we don't have gravel roads here, but gnarly rocky steep loose dirt). So there is a perception that it is harder on the body(all relative of course). I assured him that I would never even try to keep up with him on his rig on the trail!