Can the dog still walk? That would be a good sign at least, when the dog has a lot of trouble moving around is when you should worry, I think. Although, I have also have a pug right now who is pretty old and seems fine, even though he has some trouble walking.
-Flashback
This reminds me of our dog that died at age 15 or so, but I think she was in worse condition then yours (she had a tumor in her stomach and some unknown fluid building up). Basically for a year before we had to finally put her down, she wasn't able to climb stairs anymore, so she'd bark really loud when she wasn't able to get up when we went to bed. For awhile one of us would bring her upstairs but eventually we got a big pillow for her downstairs. For the last few months of her life, you could tell she was in pain and had trouble breathing.
A day before my 14th birthday, we got a call from my mom saying she was going to be put down. We went to the vet and said our goodbyes, then left the room. There was one good thing though, they had just found out about the fluid and drained it. Our dog was looking much better, she might not have even been in pain, it was a nice sight to see her in for the last time. This happened in January, a month or two later I found Blockland.