My little brother is threatening to kill me.

Okay, so I have a 7-year-old brother who I think needs help. He is aggressive, rude, plays violent video games (for his age) all day, has a very negative attitude, and hates almost everyone and everything. We always got along fine (with some arguments here and there) but withing the recent 2 months its gotten worst. I first noticed how violent he can be when he was 6 and threw a knife at me (it missed) after that it got better but now he is always threatening to kill me and waves knives or scissors in my face. He is very easily angered and once almost tackled a 4-year old for stealing his toy. He yells at my mom when she does something he doesn't like or doesn't do what he says but my parents do nothing because they think this is "normal-boy-growing stuff". I don't know what to do and I don't know if my parents are right.