Dogs die from illness and injury just like people. "Old Age" how ever can typically claim a dog between 10 - 12 yrs (on average). Of course some can die at a much earlier age, due to some sort of complication or another (but that's not 'old age') .. and some can live late in their teens...VERY few make it into their 20's. I know a dog, that is 16 yrs old .. and is still doing quite well.
My pointer mix,CJ, is 16 and going strong.This is not typical. Most dogs live 10-14 years. I think God is giving CJ a long life because he was at the APL for 9 years. A couple of people adopted him but brought him back because he fights with other dogs. We had a time CJ and I but now he's docile as a lamb.
The SIZE of the dog determines the average life span. The bigger they are, the younger they die (of "normal" causes only, of course). Some little dogs have lived close to 20 yrs., but the huge dogs live less than 10 years.