My initial thoughts on your question 'what age do they stop using screaming form communication?' was sometime after puberty if we are lucky

I have screamers too - it does my head in some days. DD1 mostly uses her words now but I ignore her or tell her I don't know what she wants if she doesn't use her words. DS (who is currently 2 and a bit) is getting better - I tell him to stop screaming and use his words. I respond ASAP to DS when he does use his words at the moment just to reinforce the message where I tend to ignore and redirect his screaming. With DD1, I am at the stage where I explain to her that I am doing xyz at the moment and I will help her out as soon as I am finished but because I am trying to send a message to DS about using words, I am giving him instant responses for the moment so he can make a nice strong link between effective communication and action.

DS has a scream on him that makes you want to rip your own ears off. It is just the wrong pitch and thankfully it is getting better but I have my moments when I can't deal with it.