I haven't thought about it too deeply but imagine that most young people have no real interest in the monarchy, however with blanket TV/press coverage of the death of the Queen almost everyone is taking some sort of interest in events, by default.
It's a moment in history so many young people even with very little interest will go to the end of their road, next village, nearest motorway etc. to get a glimpse.
I'm not a monarchist but yesterday went to Green Park to see the flowers and enjoy the atmosphere.
I think once all this has died down then interest will wane... until the Coronation!