My brother is eighteen and he's very violent when angry.he's becoming short tempered day by day. he's easily angered by petty things.what could be it?

Eval: Could be a lot of things. Encourage him to get a full eval from a Board Certified Psychiatrist MD

He needs to be : evaluated by his primary physician, including urine testing for substances of abuse & referred to a psychiatrist & psychologist. If his behaviors are a danger to himself or others, you have the right to report them to the police & to take him to a hospital ER for assessment for short-term involuntary commitment to a psychiatric unit where he can be evaluated & treated. Don't hesitate.Be safe.