My "educated guess" would be that he is ill. It is not normal for them to go for days without food. Usually they only do this when they are ill, although the illness could be from many different problems anything from a parasite or bacteria to virus, age, crop problems etc. I am not a vet, I am a certified avian specialist, with certification in ornithology and as a veterinary assistant, and I have worked with birds for many years so as I said it is not a diagnosis just an educated guess, LOL. I would't try to make any diagnosis on a bird just tell you what I have learned in years of experiece.