I was once writing a non-fantasy book in which one of my POV characters was in his 30s and had to have an argument/fight with a teenager. The problem I ran into was, why would a full grown adult in modern society get so pissed off at a teenager he wasn’t related to? The character was a well-adjusted, mature, level-headed adult.
This is just one example of the issues writers run into when writing characters of different ages. I love it when books, especially fantasy, have different aged characters. I think it helps the world come to life and we see how the plot has an impact on different aged people, and how different aged people understand the goings on.
But at the same time, I think fantasy tends to do this thing where young characters are just too mature. I’ll get more into that, but let’s start already.