That was a prophecy of Jesus only, not for all mankind. Jesus is perfect because He is God. He was not conceived with an Adamic nature.
Isa 7:14 Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel.
Isa 7:15 Butter and honey shall he eat,
that he may know to refuse the evil, and choose the good.
So Jesus, who was 100% human and 100% God, in His youth had to grow in knowledge to know to refuse evil and choose good. But children with only a human nature don't need to?
I agree with you that v15 is prophetic about Jesus.
Isa 7:16 For
before the child shall know to refuse the evil, and choose the good, the land that thou abhorrest shall be forsaken of both her kings.
But v16 is not. This verse is talking about Shearjashub, Isaiah's son who God had told Isaiah to bring with him. We can know this by reading which land it was and which two kings did Judah and David's house detest. Israel and Syria, the two kings, Rezin and Remaliah's sons, had joined together against Ahaz and Judah, the house of David. Both kings were killed. see 2Kings 15-16.
H5288
נער
na‛ar
nah'-ar
From H5287; (concretely) a boy (as active), from the age of infancy to adolescence; by implication a servant; also (by interchange of sex), a girl (of similar latitude in age): - babe, boy, child, damsel [from the margin], lad, servant, young (man).
This Hebrew word is used for a new born in Exodus 2:6; Judges 13:5,7; 1 Samuel 4:21; as well as for a young man about the age of twenty in Genesis 34:19.