To me, art is the capacity to experience one's innocence: craft is how you get to that point. Maturity in a musician would be the point at which one is innocent at will. At that point the relationship between music and the musician is direct and reliable.
The relationship with music is always mysterious: when it works, you can never tell. You can never guarantee when it's going to work. You can only to put yourself in a place where it's more likely to happen.