Yes, young people do play instruments far more than they sing, and they don't often do so at folk clubs, because the clubs are mostly centred around singing. Getting up to perform on your own (or with a friend or two) for a purely instrumental set is fine, but a succession of such tune-sets would not, in most cases be a very satisfying club evening for anyone. What most musicians like to do is play together in an informal setting with other players, not for an audience but for their own pleasure. This is what happens at sessions (some of which are popular with younger players) but it isn't what folk clubs are about.It's nothing to do with age - older musicians prefer sessions too and don't often attend clubs if they don't sing.

The big difference between the age groups is that younger people are much more likely to play than they are to sing, whereas singing makes up an important part of the folk experience of older people.

Marje