Lots of very valid and interesting views on this thread, but i have a slightly different take as I do see a fair few people say in their late40's onwards (kids moved on etc..) looking for a night out, a bit of a dance and maybe a couple of drinks. Someone suggests a local motown nite, maybe a northern track gets played, they buy a few cd's etc... etc... some of them progress to a local northern nite, some get more into the music start collecting, looking for rarer sounds , more upfront soul nites etc.. weekenders sound fun etc.. So as the 65+ start to fall away there is a gradual feed of 50'ish people to takover... (I am not talking here about people returning to the scene but those who most of the music is new to) after all unless they want to sit watching tv all night what else is there ? they could well have been into say house music/hip hop etc... but they probably not going to go to the local high street club with the 20 yr olds.
Equally I cant see many 20 year olds who want to spend their weekends with a load of 50+ folk so if anything they will create an alternative scene even if it is with the same music (my daughter has recognised a few of 'our sounds' at club nights she goes to although they never call it 'northern'). How many of us when in our teens/twentys would have gone to a nite with people old enough to be our grandparents!