[the old guy] is the focus of the show
Not if
written as a secondary character, the show would (again) almost have to have a slightly older, authority figure cast member, however someone in their late twenties would do nicely, but in this show not be a main focus. If the decision is to make the young members of the cast the focus of the show, then that the way it would formatted. But at the same time there wouldn't have to be a pretense that the group of midshipmen were completely on their own somehow.
the rookie is not the focus of the show.
Except in this case they would be, targeted on the 18 to 34 demographic.
A science fiction version of rookies? ... only lasted one year.
The show I was referring to, The Rookies, lasted four seasons actual.
And in term of dramas featuring youths, Glee on Fox is highly rated, the scifi/fantasy drama Smallville is in what, season ten? Everything that CW puts out is aimed at people in their teen, twenties and thirties, five of their current shows are scifi/fantasy.
A CBS property wouldn't automatically have to be shown on the CBS network.