How old is he? Maybe he's getting stressed. It sounds like most of his anger isn't directed at you personally anyway.<br />
Try to remain calm whatever the provocation. Anger feeds off anger.
I am wondering if he had started any new medications in these years? They can have quite an effect on how a person feels and also, does he have an undiagnosed health issue which may be causing this? At any rate, please don't take what he says personally and internalize it. When he yells at you, it is because most likely he feels safe to do so, and he is probably telling you what he is actually feeling about himself? If it gets to you, I'd leave until he can settle down, as you don't need to be a whipping post.
Is it still just part of his personality that he has always had and its just getting worse or was it a total shift that is continuing and getting worse? When something small that he would normally have brushed off happens does he seem to be very very stressed out about it then goes into yelling or bitching? Has he ever blurted out something that really made no sense? Like maybe something from ages ago when you were a little kid that he had no reason to bring up, something that maybe you did not pay much attention to because he was mad... think about that one, I never noticed it myself until later when my grandmother started doing this, to this day I regret not clicking in that something was wrong before it was too late, I thought it was just her age or something and passed it off as nothing. I do not mean to scare you with this I swear! But if it's anything like what I was saying and you can get him to get checked at a doctors, do it. It might be nothing serious, but there are may things that could be happening that might need to be treated. Alzheimer's is one... but for my grandmother it was a brain tumor.
You need to talk to him and find out what exactly is eating at him. Its not just age, you can be sure of that.
I'm sorry that you're going through this. You really need to seek some professional advice. Start with asking your doctor or, maybe, a geriatric specialist. <br />
My parents are both in their mid-70s and I 've noticed that they get much more agitated at things now than they used to. Part of it is just getting Old and having pain all over (hips, back, knees, hands, etc...) They also feel less productive and less useful to society. Plus, they begin to have their friends and loved ones start dying off and it depresses them. <br />
You shouldn't let this go on much longer without some kind of help. Other siblings and family really need to be involved so that you don't shoulder this burden all alone.<br />
If you don't take care of yourself, you won't be able to take care of others.