The conclusions of this study - that musical open-mindedness drops off in the late twenties - is consistent with the fact that (pop) music creators also peak in their twenties, with a rapid decline into creative insignificance afterwards.

There's a lot of comforting analysis here on social and cultural development reasons why that might be, but the likely ugly truth is the same faced by creatives in some other areas - a clear cognitive decline, it's just too universal within those fields to be anything else than a physical cause.

With very rare exceptions old people don't make good pop music, there's no reason to expect listeners to not mirror the decline.