Hi Theresa. Do you have any idea what Barney was weaned on as in eating after he was weaned? Such as the veggies and fruits the breeder started him on after he finished weaning? If you could find that out, you may can get him to eat this to begin with and then add one or two new veggies and cooked foods to get him eating a better variety.
He's pretty young still. Ekkies tend to take a while to wean. It is not uncommon for them to take 6 or even 7 months to fully wean. It is a possibility that the breeder rushed Barney and then didn't properly condition him to eating solid foods before selling him. If that happened, you will have to be diligent in offering a wide variety of fresh and cooked foods til Barney develops a taste for the new items. And you can try a little plain oatmeal with finely chopped apples and nut meats in it slightly warmed. Offer this from a spoon. He may still be needing comfort food. If he doesn't like oatmeal, you can try some other soft warm food. Worth a try in case he is regressed a little from weaning.
Some folks don't like using it, but I do cook a little rice along with flavored noodles (these are the noodles that are made from veggies and sold for human consumption). Since I am from the US, I don't actually know what is available to you in Australia. My flock love the noodles like that and rice. When I give them the cooked rice/noodle mix I add it to lightly cooked frozen/thawed veggies chopped up fairly small. I feed cut up fresh veggies on the opposite days. I also cook lots of "birdie breads" for my flock. Some I add fresh and frozen veggies, plus flax flour and pellets to it. The other I add fresh and frozen fruits, plus flax flour and pellets. That way they get some of the good from pellets and never know it.
I have a female Solomon Island Eclectus that eats many different foods. She does toss a lot out of her bowl, this is a typical Ekkie trait. And what she may toss in the morning, she will gladly eat later in the day or the next day if offered again. She eats very little pellets and when she does she soaks them in her water.
Hope this helps a little. Just keep trying a variety of foods and even if Barney refuses certain ones, keep offering it. They change their minds just like human children. One day they hate it and the next it is the best thing they ever ate.