My parents Jack Russel is about 13 years old too. She pretty much does the same, she follows my mum around the house to whatever she is doing and goes to sleep wherever she is. She is quite deaf and also quite blind now so sometimes loses mum! My maltese shihtzu cross is 3 and when I first got her, they used to play a fair bit. The still play a little bit each time they see each other, but no where near whatthey did when she was 3 years younger.
I think it is a case of making their old age as comfortable as possible and praying that they pass away quietly when the time comes.



Edit: I am now cuddling my baby at the thought that I will have to face this one day - hopefully much in the future - it's sad isn't it.