By the time He knows enough to reject evil and choose good, He will be eating curds and honey.
The child will eat curds and honey as he learns to reject evil and choose good.
This verse situates the sign within the conditions of the land.
10Again the LORD spoke to Ahaz, saying, 11“Ask for a sign from the LORD your God, whether from the depths of Sheol or the heights of heaven.” 12But Ahaz replied, “I will not ask; I will not test the LORD.” 13Then Isaiah said, “Hear now, O house of David! Is it not enough to try the patience of men? Will you try the patience of my God as well? 14Therefore the Lord Himself will give you a sign: Behold, the virgin will be with child and give birth to a son, and will call Him Immanuel. 15By the time He knows enough to reject evil and choose good, He will be eating curds and honey. 16For before the boy knows enough to reject evil and choose good, the land of the two kings you dread will be laid waste.