The OP conflated two issues:

1. Getting young people into folk music in the first place.

2. Improving the demographic balance of an individual club.

You can get, and are getting, youngsters (teens or early 20s) into the scene but you won't get them into a club where the next youngest person is complaining that the change in pension age means that they are having to wait for their bus pass.

If a club cannot maintain a demographic balance it will eventually fold even if the local scene as a whole is healthy and active.