I think that's a great way to have skills. It's realistic, because there's only so much you can learn alone, and it improves game balance by a character not being able to over specialise a skill too early and spoiling the game. Also, the "do a quest for a skill" idea is plausable. In fact, it could be the training! "Climb the highest peak and bring me back the flower that grows there." The climb is such a struggle that you have to invent new methods of climbing to make it up there, but without the order to retrieve the flower, youd never try. Mind you, you'd be pretty pissed after paying 500,000GP and finding out that the sage doesn't train you personally...
