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…
Even in pop music, I'd argue that artists are doing very little of the actual heavy lifting compared to the producers and the writers. Pop singers have a much shorter shelf life than producer/writers due to the importance of image in appealing to younger fans. See https://en.wikipedia.org/wiki/Max_Martin for an example.