Its very normal for this to happen to an older dog! Just like people when they get old and can't hold their bladders anymore..I would start diapering him(belly bands), that's what my Mom had to do with her dog, he lived to be 15, but, he got to where he couldn't hold it anymore, it's really sad..
My golden retriever also got like that when she got up there in years...I don't know if you could train him to pee pads now or not, mine have used pee pads all their lives, so, that makes it nice, but, when they have always gone outside, it seems almost impossible to train them to use the pads...I think the vet would tell you the same thing, that with his age, this is VERY NORMAL