it's not either 15 or 18 it's 15 to 18, which means you can choose 15, 16, 17, and 18

I edited my starter since you seemed confused about the age range. I'd rather not have people think I will only allow people to be two ages.

though I could lower the age down to 13 and include middle school, which would mean the game is rated Teen, and that would make those characters still have the ability to run into other characters while at school.
(I came up with this because of your statement of kids in high school being 13, so thank you)