Isaiah 7:11 makes it clear that this boy's birth will be a sign to King Ahaz. The boy would be named Immanuel, meaning "God with us," so Ahaz would know God had not abandoned his people, and would deliver them from the armies that were poised to attack. According to verse 14, the boy's mother was already pregnant when Isaiah and Ahaz had this conversation, so Isaiah was not referring to Jesus in this passage.
However, Matthew, writing several centuries later, saw the birth of a child as a sign, saw the parallel with Jesus' life, and applied this passage to Jesus--who, in Christian theology, is "God with us" in the fullest sense. (Matthew often uses passages from the Hebrew Bible this way. For example Hosea 11:1 speaks of God calling his "son" Israel out of Egypt. Matthew applies this text to Jesus as well, when Joseph and Mary take Jesus to Egypt to escape Herod, then return after Herod's death.) But what Matthew has identified is not the primary meaning of this text, and the passage as a whole should not be understood as a description of Jesus.