Thats a tough situation. I have a younger brother around that age, he's 13 but that really does'nt matter. He's not violent but he thinks he can do whatever he wants.
It sounds to me that he may have a psychological problem, not like he's a nutcase but something that he would need to see a psychiratrist or a
conselur. It seems to me that he's holding back on something, maybe your divorced or your wife died recently? He's become careless about life and
has be come destructive. I urge you to check if he's into drugs or alcohol as well since those do alter moods. Something is defintly troubling
For how long was he like this?