i aree that it i a good skill to have to be able to communicate his feelings. I know it is not the same thing but at school where i work (secondary school) i deal with children who get 'wound up' very easily. In lots of cases their anger comes out in the form of violence. One of the ways that this is dealt with is for them to take an 'anger management course'. Part of this involves teaching them how to express their feeling verbally (in a non prissy way iykwim)
Pupils are given a 'time out' card which allows them to just take a minute outside the classroom to calm themselves down.
By expressing his anger it seems like your ds is doing this.
Sorry to go on, i just wanted to shae my experience and hopefully make you feel a little more reassured. sorry for the waffly post.
btw my ds is 10months and already does the fist clinching and gritted teeth tantrum!