Physiological condition, rather than chronological age, determines whether a dog is mature. Aging begins when the body's systems start to slow down, when cells deteriorate faster than the body can repair them. Though large breeds tend to age faster than smaller breeds, the mature years generally begin at around 7 years (5 years for large breeds). If you feed your dog a diet designed to address the nutritional needs of his age, you can best maintain his overall health and well-being.
As your dog ages, it is important to detect and address with his veterinarian the telltale signs of aging or disease: a dull, dry coat and flaky skin, joint stiffness, energy loss, weight gain, increased water intake, digestive problems, and frequent constipation. These signs, among others, may be caused either by normal wear-and-tear or perhaps by the onset of disease. In any case, detecting and addressing them early may give your dog a greater chance to stay active and healthy.
When and how your dog responds to the aging process has a lot to do with genetics and environment, but nutrition plays an equally important role. The quality of food and its ability to maintain and nourish your dog's cells can help promote a long, healthy life.
As your dog ages and his systems become less efficient, he relies increasingly on the food you provide to make up for his body's shortfalls. According to Michael Hayek, PhD, an IAMS research nutritionist who specializes in geriatric nutrition, 'Aging dogs need the same nutrients as younger dogs; however, the quantity or the way the nutrients are provided may change.'
Does your mature dog sniff at his bowl and walk away instead of digging in? You may think he’s just being picky, but it’s important to keep an eye on how much he’s eating — especially if he’s a senior. While age-related diminishment of the senses of smell and taste may account for some of his disinterest in food, appetite loss can also indicate a serious medical problem.
“It’s important to give your dog enough calories because weight loss can be debilitating to senior pets,” says Wendy Brooks, D.V.M., who warns that a loss in appetite should be mentioned to your vet. A good rule of thumb: If your pet hasn’t eaten in a day, make a visit to the vet. Here are six ways to entice your canine friend with a nourishing meal.

Many animals find canned food more palatable because they like the taste and texture, Brooks says. You can top their favorite dry food with room-temperature wet food.
Dogs like a warm or room-temperature (not hot or cold) meal. Avoid serving him day-old wet food from the refrigerator, and keep his food away from heat. Another reason he might not be eating: It's too hot outside.
Dogs prefer consistency when it comes to their food. Don't change every day, but try a new flavor, such as lamb or chicken, and see if he responds (it may trigger his sense of smell). To avoid an upset stomach, introduce a new food by mixing it with his old food in equal increments each day.
Common mature-dog health issues, such as arthritis or joint pain, can make it difficult for him to access his bowls. Keep food and water where he spends most of his time. Put a water bowl on all floors of the house, too.
Older pets are at a higher risk of dehydration. Provide a clean bowl with fresh water at all times. It will help prevent disease, such as a kidney condition, and aid in digestion.
Dogs are people pleasers. If you see him eating, give him a little verbal reward. He'll know it makes you happy and will repeat the behavior.