When I got my chihuahua he was 6 years old and only paper trained. It actually only took me a couple weeks to leash train and house break him. I used a baby gate and kept him in the kitchen and crated him when I was gone. Actually I did the same with Charlie (min-pin) when I got him. He was 2 years and he was harder to house break, it took him a couple months.
I really don't have any good advice for you, I just wanted to let you know there is hope.