I've seen you say before that you thought Bale was dodgy for a long time at the start of his Spurs career but I really can't agree. His initial games showed clearly how dangerous he was. He scored against Utd, Arsenal etc before he got injured and I remember getting very excited about him - I'm sure others were too. As an 18/19 (?) year old he clearly looked like he had something about him in a way that Rose has, so far, not (in a Spurs shirt, at least).
I really do believe that most of the really decent players who I've seen as youngsters were clearly good right from the off. If anything, for me, they tend to look better than they actually turn out to be when they're young - keen to impress, bags of energy, unafraid.
Trying to think of current/recent players and how they seemed to start with: King, Dawson, Walker all looked good from the off. Lennon looked great right from the off, Livermore so-so, Kane so-so, Carroll looked exciting from his first few games. Mind you so did Rohan Ricketts, Adel Taraabt and I distinctly remember thinking during the course of one pre-season game, that Dos Santos, not Modric, was the signing of the summer.
By the way I'm not claiming any special insight. I bet most fans would've agreed with me at the time that Lennon, say, looked a bit special and that no matter how much time we gave him Jonnie Jackson, say, was never gonna cut it at this level. I think that's it's pretty clear a lot of the time.
Perhaps Rose'll prove me wrong - I can't think of a single player right now who looked quite average to start with when they were young but grew into a really good Spurs player*. Maybe Rory Allen is still hanging around somewhere being promising with his U-21 cap or two...
*Maybe Crouch could have been a contender for this title, if I'd ever seen him as a young player. Or he'd grown into a really good Spurs player. Only kidding! Always had time for Crouch. Kaboul also looked a bit dodgy when he was young but it looked more like his decision-making more than anything - his heading and tackling and comfort on the ball going forwards was clear from his first few games.