I think the part in the book of Luke at chapter 2, where Jesus, as a child, stay in the temple after Passover to discuss with the priests and how he answers his parents: "is it that ye sought me? wist ye not that I must be about my Father's business?" (Chap 2, verse 49 of the KJV) seems to indicate that he was already aware of that, even if he then waited his 30s and meeting with John to start his work.