Ok, Not an expert either. But I had 2 african grey's sofar and the 1st one flew away. Not long after I got myself another.
What I have learned is to feed them "Exact-Hand feeding Formula" as long as possible. Keep them away from large pieces of food unless they are up to date with weight. This is because when they learn how to use their feed to eat they get stubborn. Meaing that they wont eat their much needed grow suport.
I can tell you right now that when I bought the first parrot it was only 450 gramms before he departed. Now having a 2nd one, I changed all restrictions and its "on-par" with a real parrot feeding the "puppy"
So, yes, I have got now a 1 month younger parrot who's weight AND seize exceeds all I have ever seen sofar...
Oh, yes! And he is Soooooooooo sweeeeeeeeeet!