I have trouble with the "on average" part, sorry. I want to go into the conditions that make each genre age well or not, and compare and contrast them, and come up with a complicated algorithm that predicts for each genre what elements, in what combinations, will make the story age well or badly.

But when I go to think which genre has more essential elements that make the stories vulnerable to bad aging, I get antsy and want to change the subject.

And there you have the reason why I haven't been so vocal lately. This always happens to me nowadays.