Here's the thing - when I was 18-20 I used to workout and I don't recall having any sort of problems with any lift. I don't even know if I ever did BB press back then.
Fast forwards 12 years, I'm 32 and I've been working out for over a year. About (roughly) 8 months ago I joined a gym with barbells (before I was at work, with DBs and machines). I've really just started doing BB overhead press.
So I'm not entirely sure if it's related to the impingement or not. As to my hands/posture:
I arch my back and my hands are wider then shoulder width. When I bring the weight down to my chin, my upper arm and forearm form a 90 degree angle. I think I'll try to get a video together, which I've been meaning to do for my deadlift as well (to see if it's improved).
You might be right. I don't know - I suspect if I get a vid up that would help everyone with the diagnosis.
Twice as much a week, I'd say.