Good for you! My cat lived to be 18 as well- the main thing that I
watched was that the ash content was low- he did get blocked as a young
fella and had to go get emergency treatment adn would have died without
it. I fed him decent food, and as he got older I did give him some
scraps....
I now have this big fatty tabby and my two Bengals- the fatty is fat no
matter what I feed him (including diet food, high quality) and he
really does not eat much. He is just a big, twenty lb tabby- the vet
said that he is fine. The one Bengal can be touchy because of his
stomach, this is when the food does matter! Do try hemp seed oil though
if you want- this give essential fatty acids that they don't get
otherwise! If your cats are living that long, obviously you are doing
something right! After reading this, I am not going to do anymore
research on Costco food- if it's good enough for the breeder, it's good
enough for me! I think those other foods are just over priced and if
you compare the ingredients- Costco is the same as Iams!! Take care!