I'm not a veterinarian, so I can't diagnose bird health problems. I can say that if your bird's poop is black when it's first released from his body and if he hasn't eaten anything unusual that could add colour to his poop, he probably has an illness of some kind. Black poop is not a normal sign of aging, though it's possible that your bird developed an illness partly because of his age. It's important that he visits a vet for a diagnosis and treatment soon.
The illnesses that I know of that can cause black poop require veterinary treatment. They can't be treated with home remedies, though conditions at home may help a bird to recover while he or she is receiving treatment prescribed by a vet.