According to professionals, senior dogs need adequate protein and a little more fiber. I peel the apples to reduce the fiber since my maltese are very small dogs. Fiber is not considered an essential nutrient in the diets of cats and dogs, but it is present in almost every commercial pet diet. Natural antioxidants in pet foods contain Vitamin C. Vitamin E, vitamin C, citric acid, and rosemary are among the most commonly used natural antioxidants in pet foods. Vitamin C is provided by ingredients such as cranberries, blueberries, apples, and some other fruits. Dogs and cats do not derive any energy from fiber however improved colon health is a benefit of having fiber in the diet.
Some things that are really good for dogs are Blueberries (fresh or frozen), baby carrots, apple wedges (no seeds), bananas, melon, and pears. The ASPCA has a good list of people foods to avoid feeding your animals.
Pits from Peaches/Plums: Can cause obstruction of the digestive tract.
Grapes/Raisins: 10 cases reported to the ASPCA Animal Poison Control Center (APCC), each dog ingested between 9 ounces and 2 pounds of grapes or raisins. Symptoms include vomiting, diarrhea, abdominal pain, and lethargy.
Dogs can suffer kidney failure after eating of large quantities of grapes and raisins. The key words are "large quantities", and of course the size of your dog. The reported adverse responses to grapes and raisins are not from pets eating the occasional single grape or raisin. The cases of kidney failure involved ingestion of 2 ounces to 4.4 ounces of grapes/raisins.
Giving your dog 3-4 at a time could get you up to that 2 ounce limit.