Playing devil's advocate here, some would say that whilst K Hunt is a good example of a player who has handled the physical rigours of first grade, maybe, given his much publicised issues off the field, he wasn't really 'ready'.
This comes back to coaches trying to shield young players not only from playing against men, but also from the emotional and mental impact that fame brings with it. You go from being a nobody to playing alongside your heros, earning millions of dollars, face on TV, being recognised wherever you go.
It takes a real level head to manage that and the weight of expectation that goes with it, especially from such a young age.
It's a tough one. Everyone loves to see the new young gun tearing it up, but there are so many sad stories of kids going off the rails, often turning it around in their mid 20's when they mature. I'm not sure where I fall on this, if the kid seems super mature from such a young age, (Haas and Fafita seem more mature that TPJ :P) then maybe it's fine.
I'd like to think the Broncos have the right culture in place to manage this and the KHunt would not have gone through what he did if he was still here.