|I found old people!|
This is so beyond arbitrary. I've got characters across every age range...of course, the majority of them, including major characters, fall into the teenager/adult trap, but I have my reasons for preferring those age groups.
For the sake of this, however, I'll keep the answers limited to major and higher-minor characters.
The oldest character is obviously one of the Gods in Nagnomei. They're each over 4000 years old, which right there makes them older than any of the sorcerers from CROSS// who cap out at around 2000 years. (And that's the ~older~ ones.) For non-immortal characters, the oldest semi-prominent character is probably Regina from CROSS//, who, according to my notes, is 66 at the start of the series. I enjoy writing older people, or at least people who have lived for a long-ass time, because they have that certain cynical edge to life that I relate to. A lot.
The youngest character, who is not a cameo as a child, would be Jessie at her debut in Nagnomei (15), or, if you want a supporting character, Kana (14) mid-way through the series. The important thing to keep track in this series is that, although many of the main characters are in their mid-late teens, they are almost adults in their society and are treated as such. (Seventeen is the legal adult age.) This can account for why some of them may act more like 20-year-olds as opposed to 15-year-olds. It is not uncommon in the kingdoms for children to be treated as young adults the moment they reach puberty, as mortality rates dictate that efficient families need more adults than children. This is not that much different than from how our own Western societies treated teenagers not even a hundred years ago. I actually enjoy writing characters in this world at this age because it's interesting to play with the notion of being an adult while still trying to hang on to the comforts of childhood...
...Says the 22-year-old.