My oldest GSD is only 7, so she is barely in her senior years. I feed her a mix of BLUE BUFFALO salmon or chicken 1.5 cups per day mixed with salmon/fish soup or skinless boneless chicken breast soup with pureed veggies (cabbage, carrots, broccoli, spinach, cauliflour) and seasoned with minced garlic, turmeric, curry and parsley.
I will switch off with BENEFUL Chicken or Salmon using the same home made fish soup or chicken breast soup with pureed veggies.
I stay away from duck, lamb and beef.
My dogs get fed ONCE a day in the early afternoon; in the a.m. and mid morning they get high protein doggy treats on which I will place a small amount of pure peanut butter or pure almond butter--- no sugar, no salt, no additives.
I also give my dogs fruit smoothies-- bananas, coconut milk, spinach, pineapple, apple, carrots and ice cubes with some yogurt.
Except for the doggy kibble, I eat what my dogs eat.
My dogs live long and healthy.