
Breed (Genetics) and size/weight are the biggest factors in life expectancy, and diet as long as it is adequate will not have that much bearing.
I know a fair few border collies fed all their lives on middle of the range completes that have lived 16+ years, and the same owners Terv is 15, with the most rotten teeth, but otherwise still pottering about, albeit stiffly.
My own dogs range from 3 to 11 1/2 years, and the oldest ones Dam is 14 and her Grandmother was definately alive at nearly 16, all fed on complete foods.
The thing all the bove dogs have in common is being medium sized of similar weight (18 to 25kg). some of the small breeds live a good few years longer than that, and most dogs over 35kg are considered old at 10, whereas I am just starting to noticxe my oldest one getting a bit tired on our longer walks, and that she had lost a bit of muscle on hidquarters at 10.