It’s not surprising, really. By 30, you’ve probably found a ton of music that you like, so there’s more to re-listen to and less reason to seek out new and different music. When you have a huge catalog of music that you know you like, why take the chance of something you might not?
Plus, we no longer have to be desperately searching for music to define who we are, or to reassure/impress our peers with our up-to-date tastes.
The gender differences are more intriguing. That there are more female vocalists in the top right now I shouldn’t think would be much of an explanation. Why wouldn’t men like female vocalists?