I think elderly dog benifit from suppliments because,
Immune support, Omega 3s and nutritionally rich food they can easily digest.
Dogs need greens, veggies and herbs
A good dog supplement is cheaper than drugs or a sick dog.
So it is good for there health.
So Check Out

Aging dogs have special nutritional needs, and some of those can be supplied in the form of supplements. A large percentage of older dogs suffer from arthritis. By feeding a daily supplement containing glucosamine and chondroitin, you can help support joints and minimize damage to the cartilage in the joints. These supplements have been shown to be very safe and effective and do not require a prescription. If your dog is not eating a complete balanced diet, then a vitamin/mineral supplement is recommended to prevent any deficiencies. Some owners like to feed antioxidants like our Antioxitabs. As mentioned earlier, a fiber product such as wheat bran may help to reduce the incidence of constipation.

Whether they benefit or not, that’s what you need to find out.

Yes they can. Just like humans, dogs lose certain vitamins and minerals as they age. Supplements are a great way to replace them.

That would depend on what you are supplementing for. Example: elderly dog with joint problems/arthritis can benefit from a Glucosamine-MSM supplement.

Yep, Hell yes, but find a holistic vet to talk to. They’ll tell you what is suitable for dogs or where you can get what your dog may need.
Good luck.

edit: The vet can tell you appropriate amounts for your dog, that will differ from humans.

yes

Yes but check with your vet as a good quality dog food does contain the correct amount of vits they need so you don’t want to overdo a particular vitamin in case it damages their liver or kidneys.

It doesn’t depend on how old the dog is. If your dog is very old, the supplements will not be absorbed.

Sure they can benefit. It is like an older human, they need a little extra bang that food alone just can’t provide.

Absolutely! These two are probably the most commonly used…
Glucosamine and Chondroitin-for joints/bones
Fish Oil-for skin/coats

Older animals tend to absorb fewer vitamins, minerals, and electrolytes through the intestinal tract, and lose more of them through the kidneys and urinary tract. Also, some older animals eat less (due to conditions such as oral disease) and may not receive their daily needs of vitamins and minerals. Some evidence in other species suggest that antioxidants such as vitamins A, E, and C (beta-carotene) may play a role in protecting against some normal aging processes.
Talk with your veterinarian to determine which supplements may be beneficial for your dog.