Are the "youth demographic" really only attracted to shows about young people? I think Star Trek did just fine with the youth demographics without having to have exclusively young people. Was Picard a turn-off for young viewers? Was O'Brien the reason fewer people watched DS9? Is a little bit of gray hair scary?
Frankly, if the characters are going to be cadets in all but actual practice, why not just make them ensigns and post them to starships?
What's the advantage of having them be cadets? Seeing Future Earth? That's not enough to draw a regular audience, is it? And why should viewers who aren't
in the "youth demographic" (the producers would want to attract those viewers, wouldn't they?) be subjected to stories driven by teen angst? Teen angst is artificial in drama and
in real life - who wants to watch it?