There's part old subjective rant part truth in this; I've listened to countless hours of any genre of music [0] and this generation fails to appeal to any part of my brain most of the time it's flabbergasting. Every time I hear something that makes me feel 'yeah.. finally' turns out it was some old tune I just didn't know about. There's no feel, no harmonic subtlety, no grit .. I think the pop ethos of music died a few years ago, it doesn't represent something sacred for society, it feels like a commodity.
This happens to most: "I'm not getting old, the music is getting worse! Really!!"
Nope, you're just getting older and more out of touch, and your own out of touched-ness stops you from recognizing it as such. It's kind of like the Dunning-Kruger effect that way.
There's a ton of variety and good music out there if you bother to look. If you can't find any, that says something.
I think part of it is that people become more calcified in interests and habits as they get older. For example, when I worked at Costco I noticed how much more stubborn older customers were -- contrary to stereotype, younger customers were generally far nicer and more flexible. In high school, people my age were open to all sorts of things; now that I'm in my 30's, people have more established interests. My own wife has pointed out that I'm fairly particular about friends now sharing similar interests.
Meh, I didn't have to look before to get interesting music. And my interests are more diverse than when I was young. I span the whole music spectrum. From old to new, pop, kitch, complex, simple, classical, thrash, whatever. Today's mainstream is really poor.
to give you a weird example, some girl on youtube decided to cover knight rider's theme with violin's only, you can see how this simple tv show got very interesting harmonics and melodic emotional structure.