I feel like the more obvious explanation is that older developers already know the languages young developers want to learn. JavaScript, C++, Java and Python are widely used and knowing them has a much higher return than Go or Kotlin as first or second programming languages.<p>If you have been a developer for 10+ years there's a good chance that you either know these "older" languages or you know that you don't need/want to learn them.
It doesn't surprise me that those languages are favourites for that age bracket (18,24). Python C/C++, JavaScript and Java seem to be what's taught (or assumed) in most CS degrees. You have to take into account that only small group of students in that age bracket would venture off and extend themselves. Most are content with knowing just the "standard" languages.