What are the signs of a dying pet?

I felt exacty the same way when me cat died. If he's getting arthritic, and not playing very much anymore, it's definently a sign that he's getting old. But who says he can't get old normally? Just let it play out naturally and dont put him down unless the vet says its absolutely necessary. He probably loves you just as much as you love him. It would be mean to take that away from him... I'm sure he's going to have a great rest of his life. Cute picture, btw. Good luck, mate.