God is no exception. But, just as a normal father is not the same person as his son, neither is God the same as His Son, Jesus. When you look in a mirror, you see your image. In the same way Jesus is not the same being as God. He reflected God's character to men.
Fathers always exist before their children.
God has always existed. But Jesus, as His Son, has not. Jesus did not exist until he was born. God gave His Son. God and Jesus are separate beings.