Small dogs are generally considered to be “mature” or “senior” when they are about seven years old, according to the American Veterinary Medical Association. Because large breed dogs typically have shorter lives, they are often considered senior by the time they are five or six years old. But it absolutely depends on your pet and their activity level, lifestyle, and any medical conditions, says veterinarian Barbara Hodges, DVM, program director of advocacy and outreach for the Humane Society Veterinary Medical Association. “Many older pets do have mobility limitations and keeping them lean can be helpful in that regard, so a lower-calorie diet may be appropriate for them if they are wrestling with weight issues,” she says. “Your senior pet may also have medical challenges such as kidney insufficiency, in which case he/she may need a special renal diet with fairly significant protein restriction. It is therefore important to involve your veterinary healthcare provider in discussions about your senior pet’s evolving dietary needs.” However, not all dogs should be switched to senior foods, cautions McCarthy. “If your dog is already on a special or prescription diet, or has a sensitive stomach, you may want to continue feeding the same ‘adult' dog food instead of a senior dog food to prevent any issues by switching diets,” she suggests.