Haha, I'm 16 so I have more options than everyone else! Most of the characters are 17 or older!
Also,
@Oracle Spockanort said subject x is probably going to be an adult. (I'm just assuming she's Skuld here) I think there's a 50% chance she will be, depending on who Nomura wants her to be friends with.
He might do something similar to what he did with the Wayfinder trio where years passed, but they all found some sort of way to stay the same age. If he wants her to be part of a Union Leaders trio (maybe Brain, Skuld, and Ephemer), she will stay the same age as the other members of the trio. I don't know how she would stop aging, but with Nomura, there's always a way. If he wants her to be part of a trio with Axel and Isa, she will be made to be the same age as them.
I went on a tangent on something that has nothing to do with the topic of the thread, (probably belongs on another thread,) but what Spock said got me thinking.
Anyway, my waifu and husbando I'm going with (for now) are Kairi and Ventus.