I have not been angry much of my life.
At 35 I am FINALLY feeling anger, and boy howdy is there a lot of it. I am at times having pyschosomatic symptoms from it.
Talking about it in therapy (most of it is not A related), most of it has been there from way before but the implosion of my relationship with A has helped me to access it.
The Dance With Anger (book) has helped immensely. How Do I Forgive You and the Freedom not too also has helped (Janis Abrahms Spring). Honestly for me I am learning that there is an emotion (which is okay), and what I do with it (which is often where I get caught up).
I do some writing, but a lot of therapy, bringing it up as a topic in Al-anon (which is a way for me to see how others do it and gives me a chance to try).
For me it could not happen quickly. I had to feel it, be present with it and in a way thank it (it has allowed me some boundaries I was not capable of before). Beating myself up for feeling it, only made it worse.