I'm 19, and my main comic protags are 10-11 years old, with one 14 year old. anyone older than that is a side character.
most stories i've written in the past featured characters younger than 13, mostly because i've always enjoyed writing child protagonists and the only books that interested me when i was little were about kids my age. you can have them facing danger or being introspective, and their lack of experience/autonomy can affect how they view the setting or the plot's events. i'm still hesitant about writing in-depth adult characters as protagonists, since i dont have the life experience myself.
but i do write short stories about teenagers around my age, and my more recent characters having been getting older; some of the stories i want to write in the future aren't well-suited to be led by children. .... plus it's probably socially unacceptable for an adult like me to be so invested in making fictional children as miserable as possible. :B