As a teenager it really bothered me that adults seemed to have lost the ability to appreciate good music simply because it was new- I vowed to make a point of regularly trying new music with an open mind as I grew older, and not to grow up like that. My own parents who loved good music when they were younger, and whose music tastes I could appreciate well, literally heard my music as basically random noise, and couldn't even process it... stuff that was deeply inspiring and meaningful to me. It seemed like such a loss and a shame that they were incapable of enjoying it.
Overall, in my late 30s, I would say it's worked pretty well. I try to spend a decent amount of time sampling new music, and my music tastes have evolved a lot over time. In just the last two years I came to appreciate two entire new genre of music I had never really paid attention to, and listen to them a lot. Although, I will admit that most of my overall favorite music is still the same stuff I liked as a teenager.
I think a lot of it is simply taking the time to sample new music, and to develop the mental pathways to process new music styles. Old people can do it just as well as young people, but generally, older people have less time and interest in doing so. Kids generally don't understand what its like to be a parent with a job, and how little free time adults have, and how precious it is to them.
Also- regarding the author's comments on "American Idiot." I've always found it amusing how American capitalism loves to unironically sell people whatever they are willing to buy, especially including rebellious and anti-capitalist products and services, which are a big business overall. Reddit is currently worth 7 billion, and caters largely to people that like to complain to one another about how evil they feel capitalism is, and especially how evil Reddit in particular is.