I think critical mass is a problem. In the nature of things a lot of young singers are only just building up their repertoire, and can find it a bit intimidating when they realise that everyone else know tons of stuff. (It had the opposite effect on me - I just thought 'wow, tons of stuff to learn!' - but I was in my 40s at the time.) I congratulated one lad on a terrific rendition of The Well Below the Valley once -

Nice to hear that song. Great version - where'd you get it?
Er... off a film.
Right. Sounded great, anyway. Do you do many other old songs?
Er, no, it's just that one.

I hope he found my interest encouraging, but I can see it might have been a bit offputting. But that's where critical mass comes in: you don't need one or two relative novices, you need a whole bunch of them, so that nobody feels they're being singled out.

I do also wonder how much it matters, though. At the two singarounds I currently go to, the age ladder certainly doesn't reach the floor, but it doesn't stop at retirement age either: our younger generation consists mainly of late 20s and 30-somethings, but we have got a younger generation. I myself started singing at folk clubs at 42 & got seriously into traditional songs five years after that. Maybe we should be asking how we can ensure a continuing supply of middle-aged old farts!