I don't rate "anyone" that plays NRL as a teenager. There are probably hundreds that have played NRL over the last lets say 20 years that have not gone on to have NRL careers or have been just very average players overall. Some players just mature earlier mentally and or physically then others. I watch how they handle themselves and see how they respond to adversity and setbacks. Are they improving from game to game and season to season? What is their body type, speed and strength for the position they play? Are they having a positive impact on the game or nonexistent or detrimental? These are some of the things to look for and then there is personality too. But that is much harder to judge correctly, because some of the biggest merkins have been some of the games greatest.
But overall, just because a teenager has made it to the NRL, doesn't mean a whole lot really other then he has beaten a bunch of his mates to the punch. But it could be for a whole lot of reasons and not necessarily that he is going to be a quality long term NRL player or he just doesn't take the next step. The trick is to stay there and a whole lot don't.
Most of us rated Robson, but only as an average player, which is what he was. No more, no less.