With all due respect, you simply do not know what you are talking about.
'First-born' is a term in Jewish tradition. The first-born is the first male born. The first-born has status of principal heir and successor of his father as head of the family. It does not refer to the order of birth of children, only male children. If I was Jewish, the fifth child, with four older sisters, I would still be the first-born.
Luke was not writing any body's tradition. He was a medical doctor and scribe for Paul. Course God sure knew what traditions of men would creep in unawares regarding the traditions of Mary. She was a wife and mother to more than just the Only Begotten Son. Mary and Joseph had children!!!!!!
'First-born' is a term in Jewish tradition. The first-born is the first male born. The first-born has status of principal heir and successor of his father as head of the family. It does not refer to the order of birth of children, only male children. If I was Jewish, the fifth child, with four older sisters, I would still be the first-born.
Luke was a Gentile...He wasn't repeating Jewish tradition...He is telling a story from a Gentile point of view...As here for example:
Luk_1:9 According to the custom of the priest's office, his lot was to burn incense when he went into the temple of the Lord.
When something was a custom or a tradition, Luke mentioned it...Luke, as a Gentile called Jesus the firstborn because he knew that Jesus had younger brothers and sisters...