Question on Ask Metafilter: Why do people prefer music from their teenage years? A lot of great, thoughtful replies. I've thought about this a lot before, but this one was sort of new to me (though it's obvious now that I think about it):
So when you're a young adult and your mind really opens up to the musical experience, you get to hear all these things in different combinations for the first time. You might never learn intellectually what a chord progression or a key change or syncopation are, or various other bits of music theory and song-construction, but your mind is absorbing them and learning about them intuitively. So when you hit your thirties you don't have the vocabulary to describe exactly why a new single the kids love doesn't excite you (e.g. "Oh, that's a I-IV-I-V chord progression and a key change one whole tone higher for the last chorus"). But subconsciously your brain recognizes that it's heard that combination of building blocks several times before, only with someone else singing and different effects on the guitars.
I assume the phenomenon has to do with new experiences + hormones + independence.