The issue isn't that older people hate new music, but they hate most new pop music. There is music, good music, that survives for many decades, or even many hundreds of years, that people of all generations love on first hearing. This music is the best of classical music, Jazz 'standards' -- stuff that passes the test of time. I do think that some rock music is looking like it will pass the test of time. For example, songs before my time, like "Sympathy for the Devil" or "Son of a preacher man" or "Fortunate Son" started out as pop, but they are appreciated by every generation since they came out. Time will tell, but we may be listening to these songs for a long time.

Here is a lovely pop song from the 1920s that appears to pass the test of time:

https://www.youtube.com/watch?v=3iYOu8MPY6Y

Here is a pop song from the 40s that has passed the test of time so far:

https://www.youtube.com/watch?v=zBrwaCjJIFU

And there are songs like that from every decade.

OK, so if everyone loves the timeless songs, what about the other songs? Well, most songs are formulaic, repetitive and just not very interesting from the point of view of time. Old people have already heard their share of that. They don't need to redo it. They are looking back at those songs from the perspective of all the songs they've heard and aren't seeing anything special. Sort of like someone who just started reading novels might get blown away by a formulaic novel because they've never seen the formula before. But the 10th novel that tries to repeat the formula will just not be enjoyable. You've seen it all before. You need something really new by that point. That's one of the things that comes with age. I was listening to Lorde's "tennis court" and nearly threw up at the lyrics.

Adding to all this is the notion that the world isn't homogeneous. There are 'moments' that are peak moments. That period of time in the Elizabethan era from 1590-1620 when Shakespeare, Marlow, and Ben Johnson were all writing plays was a golden age of English drama. It's just not the case that someone born in the later 17th or 18th Century would be able to see their contemporaries perform just as well. There are dry spells. And there are also dry spells for different types of music. The 70s may have been a golden age for rock and roll. The 80s for pop. The 90s for rap. Maybe -- maybe not, but you can't assume that there is always the same amount of timeless standards being produced in every decade, because there isn't. Some decades are more fecund than others. Some decades might not be surpassed for a very long time. In that case, it's understandable that someone growing up in the 18th Century might prefer to read plays written in the 16th Century, and if this is true for drama, there's no reason to believe that it's not true for music. Expect dry spells, during which heavily produced formulaic stuff will wow virgin ears but leave older listeners non-plussed. And don't even get me started on classical music. The stuff being written now, compared to the baroque period, it's shameful how bad it is. There are some good pieces, but the quantity of amazing music written between 1650-1750 so completely dominates classical music written between 1900-2000, and I'm a fan of Ives, John Adams, Prokofiev, Shostakovich and Satie. But it just doesn't wow me as much as Baroque music. Listen to these minor baroque pieces that wouldn't even make most "best of" lists:

https://www.youtube.com/watch?v=kkJC8p48g6g

https://www.youtube.com/watch?v=fac_egTqLAo

https://www.youtube.com/watch?v=e2SVwTjNAFg