Yeah, that's true, sorry if I came across a bit harshly.
I find it rather difficult to speculate, though, for the simple reason that some players are getting hyped up so much and than shortly thereafter completely fail to live up to expectations.
Also, being a 'star' at young age doesn't have to mean anything. Okay, Sampras won his first slam at 19, and he became to be one of the greatest ever, but Hewitt, for instance, who could've thought that he wouldn't even be in the top 20 three years later? Or Safin for that matter?
On the other hand, Roger was a late bloomer, nobody expected very much from 'that headcase' when he was around 20, and see what has happened since... so my point is that I find speculating on this not just difficult, but in fact - impossible.
But well let's see what others have to say about this!