Dogs need different diets at different ages. Yes. This is true. For example, the puppy needs milk as the major food item. You know an adult dog may need beef or chicken in addition to the boiled egg and milk. So depending on the age factor, the diet schedule varies in reality for the dogs like any other species.
Puppies need greater amounts of protein, fat, and carbohydrates than an adult dog. Furthermore, puppies need more frequent feeding schedules in a day, unlike an adult dog. The movement-based requirements of diet are more in the case of puppies since they are often more active than adult dogs.
Elder dogs need restricted protein but the protein needs to be easily digestible and easily assimilated in the body. The diet schedule should have an ample supply of water for them. Feeding aged dogs too much protein may finally lead to overburden to the renal structures and ultimately, the dog may end up damaging filters in the kidney.
The immune system for these dogs can easily be compromised due to different factors. Similarly, elderly dogs need less food only because the movements of the adult dogs are highly restricted and hence, they have to spend limited energy.
Female dogs in the pregnancy stage need not be fed a full stomach since it may cause some discomforts to the animal. However, the pregnant animal and the nursing animal need a special type of food items that deliver a balanced type of nutrition with proper supplementation of vitamins and minerals.
The nursing animal with puppies need to be fed with enough amounts of calcium and hence, there will not be any calcium based deficiency and the bones of the puppies will be strong without any curving.
Just like us humans, they do make food for senior dogs which provide all your dog would need. I personally do not have any senior dogs however from what I have read that Blue Buffalo Senior Dry Dog Food is the best on the market.