As a person in my mid 20s, and a folkie (and *filker* (filk is Science Fiction folk song)) for sure, I felt I should speak up here.

In my experience, which has mostly been in southern California over the last decade or so -- there are a lot more people older than me than people my age in the community -- but there are some of us younger folks, too. There is a supply of younger trad. musicians, and various younger filkers, although many are not as regular attenders at events as the older people.

As for a shared canon... it's hard to say; there's still a strong feeling that "people our age don't like that old people's music" (i.e. the Beatles ;-), or Dylan ) -- but at the same time, there certainly is an awareness of a shared history of songs.

I can't speak with great knowledge about this, as I'm typically more comfortable with people older or younger than me, so I have a somewhat limited experience of folks my own age, in or out of the folk scene. But hopefully this will provide an additional perspective.