I don't know how to write characters who are fifteen and under because I don't remember what it was like to be that age, even though it was almost three years ago haha.
But you should run that by your coach, Tally. See if you should age him up or try to make him sound a little more vulnerable. I know young teenage boys are always trying to act tough and grown-up when in actuality they're still little kids, in a way. But then again, Emil has been through some pretty messed up stuff, so his experiences does harden him a little.
Part of me wants to say that it would be a good idea to make him a little bit older, sixteen or seventeen perhaps, but...I don't know.