Plenty of birds are fussy eaters, and there are different methods of getting them to eat the food they need. Nuts and apples are healthy, but the bird HAS to have more gaiety than seed, nuts and apples. Our bird wouldn't eat anything besides seed/pellets and table food when we got him, and it was extremely difficult to get him to try any kind of fruit or veg (so much so we started consulting the vet about what to do with him).
The first method is to eat some of the food yourself right in front of the birds cage (preferably in the AM before his morning feeding so he's hungry) and really make a really BIG deal of how yummy it is. It helps if you have another family member too, who you can share the food with and you both act SUPER excited and really play it up. See if he gets him intrigued and wants to try some of what your having. Parrots are flock animals, so if they see a perceived flock member (you) eating a food and enjoying it, they may be more inclined to try it. This is usually all most birds need to be encouraged to try new things and enjoy them. Many older birds have simply never had these things in their diets and may not even realize they are food or taste good. And if there are a few things he doesn't like, that's ok, but he needs to have at least 6 or 7 types of produce other than dry food he will eat on a consistent basis for him to have enough variety (and the more, the better of course).
The second method is trying to "sneak" the healthy food into their diet. Things like mixing finely chopped veg into the food so they have to eat some to eat their other food or offering them specially baked "birdie bread" or "treats" that have fruit and veg mixed in. I am personally not too much of a fan of this "sneak it in" method because, yes, the bird is eating some produce, it is still not eating enough and you still have not addressed the underlying issue of the bird being unwilling to try new foods. It's kind of like getting a picky kid to eat some spaghetti and patting yourself on the back for "sneaking" in veggies because the sauce has tomatoes and onions or whatever in it. Still not enough to be nutritionally relevant overall and still doesn't address the picky eater issue, though some may disagree.
The most "harsh" method (and a lot of people are not fond of it) is to let the bird go to bed hungry so to speak if it will not eat it's fruit and veg. This is a last resort and one you MUST consult with a vet on so you can come up with a professionally guided action plan specific to your birds needs. We had to do this with our boy because nothing else worked and he was not getting adequate nutrition, and hadn't been for probably his entire life. He actually PICKED the chunks of fruit and veg out of the "breads" and treats we made him then flung them and just ate the bread part when we tried "sneaking" it in or just refused them all together:20: And he didn't care if we ate fruit, he wasn't going to touch it. The vet outlined a healthy weight range for us, instructed us to weigh him daily to make sure he wasn't loosing too much and said to only offer fruit and veg until he got hungry enough to try. Hunger is a strong motivator, and it didn't take long for him to get over his aversion to the produce. We went about 5 days without giving him anything else but produce, carefully monitoring his weight as-per vets orders, and tried him on every fruit and veg we could get and was safe for him to eat. We took notes and recorded ones he liked better and at the end of it, the bird learned this not all this stuff was yucky or inedible. He still has to get his fruit first, and once he's eaten a reasonable amount, then he gets his other food or he won't eat the fruit, but thats better than him refusing it all together. He is much less picky about the veg., but I have no idea why that is.
As for calcium, you can buy powder supplements to sprinkle on the food, or liquid supplements to put in the water. I would consult with the vet on which is better, and the appropriate dosage.
