When will Starlin Castro make an impact for the cubs.?

Now listen up guys I like all cubs fan want any talent that can come on the scene and make an impact. However I hear every one saying that he will start this year. I feel that Castro has had a rather nice 2010 spring campaign thus far, I think he's batting pretty close to 300; and is improving quite steadily, on all aspects of the game!!!! However the guy is only 19 years old and when you have Ryan Teriot as your slatted number one why would you bring Castro to start this soon. Now I do believe that he should be brought up at some point in the season to gain some experience but how long do you guys think he should alternate back and forth between the bigs and the minors before making him an every day man? what's your thoughts guys ?