Dogs over 7 years of age are often considered seniors, but this varies greatly by breed. I assume you want to know when you should switch to a senior dog food. A much better way to go is to prepare a dog food for your dog. All a dog needs is meat, bone, omega-3 fatty acids and a probiotic. Meat and bone you can get by using chicken leg quarters, baking them in trays in the oven at 350 F for 75 min, letting them cool overnight in the oven, pouring the liquid into a container and refrigerating, and removing the long bones, the leg bone, thighbone and fibula, and leaving the meat, cartilage, skin and the other bones for the dog. If the dog is overweight, remove the fat from the refrigerated liquid and mix the jelly-like aspic into the rest. Add cod liver oil or flax seed oil for the omega-3 fatty acids, and add plain, unsweetened, unflavored yogurt for the probiotic. Adding leftovers or tablescraps adds some variety.