It really depends. There are so few pure Vos breeders left for one thing, and the other is that not all babies are fed the same while being hand fed. So to generalize, I'd say if the bird weighs more than 425 at 6 months and even a year as long as he's been gradually gaining a few grams a month, he is fine. He *might* get over 500 when he's a 10 or 15 year old bird. Maybe sooner. Especially if he flies a lot and builds up muscle mass. My heaviest bird is a female though.