From my perspective, you really are stuck in a bubble of old music, whether or not those takes are "new". Modern art music is old music. Jazz, even the most forward-thinking of forms, is old music. I don't think you're able to draw the conclusion that young people aren't interested in music from the concerts you attend, because you are simply listening to old music.

If you want to see hordes of young people who are genuinely interested in music (new music), you'll find them within the sprawling umbrella of club music. Not your local top 40 pop club, but the underground places.

Young people who are interested in music are focused on novel atmospheres/noises coupled with danceable rhythms. They're not interested in harmony, chord progressions, or sounds created near-exclusively by acoustic or electroacoustic instruments. That's the purview of old music, and that's why you'll only find it in music schools (which are fantastically archaic) + old people.

On that note, I'm willing to accept the hypothesis that the "average" young person today is less interested in music than in the past. It's probably true. But your evidence is... well, I think in a bit of a bubble.