As another older poster here, I'd have to say that I've separated out my cd collection into a 75% that I don't listen to and a 25% that I do, and the 75% is mainly composed of CDs that I bought in my teens and early twenties. I'm willing to dig out stuff from any decade now and if an album has great songs, or the artist can take you a specific time and place with their music, then the decade doesn't matter.
What stops me from appreciating a lot of modern pop music is that I don't like the vocal style, much in the way that I don't like musical theatre vocal style. If I'd grown up listening to that style all the time then yes I might appreciate that and not appreciate the Beatles, say. This is compounded by so many modern songs lacking the musicianship of previous decades, so there's no point in me listening to a vocal I don't appreciate, put onto a synth backing track or looped sample, probably overproduced, even if the song is good. On the plus side, I heard a great new track from Rodrigo y Gabriella the other day so I might have to search out their new album.