After Jesus was dedicated as a baby, Luke says:
And the child grew, and waxed strong in spirit, filled with wisdom: and the grace of God was upon him.
Luke 2:40
After Jesus was 12 years old, Luke says:
51 And he went down with them (Mary and Joseph), and came to Nazareth, and was subject unto them: but his mother kept all these sayings in her heart.
52 And Jesus increased in wisdom and stature, and in favour with God and man.
Luke 2:51-52
As a human, Jesus had to grow, learn, and develop as any other human. At birth He was helpless and totally dependent on someone to nurse Him, change His diaper, and otherwise care for Him. He had to learn how to walk and crawl, how to talk, how to read, etc. like any other human.
I've wondered how old He was when He learned He was the Messiah. How much did Mary tell Him about His destiny? I would guess that by the time He was twelve and was taken to the Temple He would have known His destiny.
In
John 7:1-5 it says that His brethren did not believe in Him. This was late in His ministry. Some time after His resurrection He appeared to His brother James (
1 Corinthians 15:7). I wonder if that was when James came to faith?