He is a middle schooler who skips school every single day and goes out at night but no one seems to be bothered about it.
(btw i liked the anime but i find this thing a bit strange, they should address this issue)
Later in the manga there is a teacher that talks to him about it and him skipping school is also kinda talked about with his parents
Manga spoilers:
His mom is basically never home due to work if i'm not mistaken, and she's very much the type of person to be like "Do whatever you want as long as you're not in trouble", but he does talk about it with her.
Manga Spoilers:
So basically, Yamori's dad cheated on the mom, so the mom left him and raised Yamori as a single mother.
To top it all off, the mom has work most of the time and gets home at like 5/6am in the morning.
(She also appears later in the manga and kinda scolds him for 2 panels then lets it go) but yea :)