I guess — I’m pretty convinced actually — that these days more 20somethings know about the em-dash than any other generation. Not because they are actively using them, but because AI uses it for them, and then have been called out on it.
Probably
calls for a paper with a fancy title like “Generational Aspects of the em-dash”
or “Typography – A Generational Approach”
Btw: I've been using the em-dash for years, but mainly in presentations and when it makes typographically or optically.