Not saying those are the only options. Just that multiple theories are compatible with the data.

Yeah. It could be that old people aren't listening to mainstream music because we're all listening to cutting-edge, unbearably experimental atonal noise. It *isn't*, but the study doesn't say.

As far as I can tell, the study doesn't say anything about "new music" at all. It compares what people of a given age listen to with what "everybody" is listening to.

HamburgerBoxing is right, if you haven't heard the Postal Service yet you should check that out before it's too late.

The study doesn't say people stop listening to new music. It says that over time, people listen to less of the music everybody else listens to, until at age 33, they've strayed about as far from the mainstream as they're going to. (It actually doesn't show that, either, but that's what it claims.)