Hi,
This can be a difficult adjustment for such an old bird. And if he has any age related issues with mobility or vision, a larger cage is probably not the best thing for him. You can try to have the perches and toys exactly where they were in the old cage. Give him some extra treats and encourage him to play with his toys. Hopefully he will adjust. If he continues to show no signs of adjustment, you may need to try to find a cage that is similar to his old one. Case were discussed in one of our recent webinars, and the vet did mention that larger is not always better for some birds. With a bird that is out of the cage a lot, sometimes a smaller cage is more comforting that one that feels vast. You might also try covering part of the top and one or two sides of the cage to give him a feeling of protection. Since all parrots are prey species, they instinctively do not like to feel exposed. He may feel vulnerable in the larger cage.
Thank you for asking Lafeber,
Brenda