I write characters with an age limit of 14. Anything under that, and they have very minimal exposure, simply because I can't get into the mindset of people that young. They either come out super mature or super innocent, unless they are characters that aren't seen often. For example, one of my characters, Branigan, has a little sister, who's around twelve. I have a cousin near that age, and so I can generally write that age accurately for a side character. But for a main character, I need to get in their head, and that's something I can't do with people under the age of 14 (and even then that's pushing it).