I felt a call to "preach" (I now see it as a call to minister) when I was 13.
In so many words my pastor told me "that's nice.. now go sit down"
I was told of David and how it was known he would be king LONG before it happened. I was told that a calling is just that... a calling. A calling to walk the path that is before you... a calling to seek Him and learn of Him... a simple knowledge of what he plans to make of you someday.
Basically.... You have heard & acknowledged the calling.. now begins the long, long journey to fulfilling it.