Make sure you supervise him he cant climb on sills if you are there, ask your self why he is doing this what may be happening to upset him , how does his sister behave with him is he the one who instigates trouble very often an older child starts it.Could he have learned this anger from hearing others?
add is characterized by a lack of ability to focus.
Adhd, which you mention later, is characterized by an inability to sit still, a child who wanders all over the place all the time, can't sit for a reasonable amount of time in a restaurant, gets into cabinets all the time and can't be contained in a stroller, etc.
Excessive violence isn't really a classic symptom of a child with ADHD.