Good points by Rockrose. Another thing to consider is if he has had any of these problems at school. If not, then its somehow the home environment that is the trigger. In which case the clear boundaries and consequences will help. But that is also the tricky part. When he was in middle or elementary school, was he prone to these emotional outbursts? or is this something that has recently started?
Very often there are problems amongst siblings , jealous feelings ..I am thinking that it would be good to get him into counseling, get him some help in my opinion he is upset , if the older one is arguing with him, maybe you could stand up for the younger one ...
He has two older brothers. He gets along good with the 19 yr old but him and the 21 yr old argue all the time. He was doing really well at school but lately his grades have dropped. He isnt on any meds right now. I'm thinking of getting him into some karate or Krav Maga classes to use up some of his energy in a positive way.
Would you say he could be upset by anything, has he siblings ? does he do well at school, is he on any meds for anything ?