Had a thought...

A perfect example of "ages of fictional characters are arbitrary" is the AoT spin off, Attack on Titan: Junior High.

In the main series, Eren/Levi is the Bad Ship because of the age gap, while Erwin/Levi is the preferred ship because they're both adults...

But interestingly enough, it's reversed in the spin-off...

In the spin-off series, Eren and Levi are both students (a first year and third year respectively) while Erwin is a teacher and club advisor at the school.

So in the spin-off, it would be more appropriate to Frollos to ship Eren/Levi since they're both students. In this scenario, Levi/Erwin is now the Bad Ship because it's a student/teacher and minor/adult ship.

Kinda weird y'all are shipping a 9th grader with his teacher, instead of with the other kid, just saying

Which I would never say, but that's how Frollos sound.

tl;dr: Fictional ages don't matter. They can be changed to fit personal comforts. AUs exist. Ship what you want

Anyways the spin-off is ridiculous and hilarious, I liked it. Another rec if you're into the main series and if you're bored and looking for something to watch