I think it's a bit younger than 33 that people stop listening to new music. Most people's musical tastes and interests are pretty much set by the college years or maybe mid-20s, and even if they do seek "new" music, it's usually simply unfamiliar music pretty similar to what they've already listened to. The range of most tastes stretch from A to B. When most people I've known say, "I like all kinds of music," that usually means all kinds of rock/pop/rap. By sales, that accounts for the vast majority of music, but sales reflect popularity, not the diversity of the world's music -- Rock/pop/rap make up a teensy weensy slice of what exists.
Since I'm pontificatin', the post-WW2 affluence and the creation of the "teenager" with their own spending money opened this door. Before that, people grew up listening to the "adult" music in their world, whatever that was. Post war, the record companies quickly realized what a cash cow they had. Now you could extend the simple "kids music" genre up into the teens, with simple stuff made to be heard, bought, heard another 20 times, then discarded (or filed away) and the next one bought -- very different from getting familiar with Beethoven via Toscanini, jazz via Duke Ellington, and other genres with more depth then "Shboom Shboom."
This became the music people stay with for life, because it's pretty much all they're exposed to, or by now, all their parents were exposed to. Sure, there's great rock and pop, but the funny thing is, sometimes I hear a current track on WXRT, but I'm not sure when it's from. It could be 25 years old or from this year. So the stagnation of people's musical tastes reflects the stagnation of the entire music business for 2 or 3 generations by now. They go hand in hand.
Ironically, there's never been a time like today with such a range of music available, much for free (YouTube?). But availability alone doesn't motivate most of us. Exposure with a bit of focused concentration go a long way to opening up our ears. And I thought I'd just type a line or two about "sharing" this article...
Think of the changes in the music world(s) from the turn of the 19th/20th century until 1950. 50 years. Jazz didn't even exist in 1900. Or bluegrass, and classical was pre-Stravinsky and the most dissonance came from Mahler. Now compare 1965 to 2015. 50 years. Rock, for one example, dominated then, and it dominates now.