I wouldn't worry too much either. I know senior food has a slightly different formulation but I reckon it's a marketing ploy more than anything. It's only been around about ten years at most, as far as I can recall, and they usually charge a premium for it. My dog is eleven and still on standard dog food, but she also has a glucosamine supplement called Seraquin on vet's advice because of her various leg problems. She seems to be doing very well on that combination.