Asking your students want they want to learn, as Floyd first suggested, is def the way to go. Presumably something inspired them to take lessons. Teach theory in context or you'll lose them.

As for the golden oldies, I teach in high schools and I'm constantly surprised at how savvy kids are. The artists have to be 'cool' though. Johnny Cash and Pink Floyd are cool. So is The King (Elvis). There's your middle ground. Otherwise you'll just have to suck it up with the Ed Sheerans and Taylor Swifts of the world on one hand, or hard rock on the other. Hey they're kids (assuming they are kids).