we had a siamese cat that lived to 21 on dog food - she'd eat her share and the Old English sheepdog would stand over her trying to make her hurry up
having said that age specific diets (and species specific!) are probably a good idea
slightly off topic but for dogs, Royal Canin products are excellent and they are both age and breed specific
also, both cats and dogs are prone to arthritis (dogs obviously show it more, especially large breeds in their back legs) and sprinkling a little NZ mussel powder on their food (Seatone) will work wonders
