1. when mary goes to visit elizabeth, elizabeth says to her, "blessed are you among women" (luke 1:42). Elizabeth calls her a woman, - γυναιξίν. This is the traditional word for woman. Is a 12 year old a woman ?
2. (Mark 5:40-42). Then he took the child by the hand, and said to her, "Talitha, cumi," which is translated to; "Little girl, i say to you, arise."
Immediately the girl arose and walked, for she was twelve years of age. And they were overcome with great amazement.
From this passage we can see that a 12 year old at that time was still referred to as a little girl. Mary was referred to as a woman, so once again she couldnt have been 12.
3. Even at 12 years old Jesus was still considered a boy.
42 And when He was twelve years old, they went up to Jerusalem according to the custom of the feast. 43
When they had finished the days, as they returned, the Boy Jesus lingered behind in Jerusalem.
(Luke 2:42-43)
4. Though age of consent at that time was 12, sadly, this was not the norm at the time. Most women married in their mid-teens or older as you can see below.
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Though i doubt you know where your argument even comes from ill tell you its silly. The common source of this ridiculous claim is the apocryphal work "Protoevangelium of James", not from any biblical cannons, but from work that was condemned by the church and couldnt have possibly been written by the actual James. Because it was written in the mid-second century.
Dont make baseless claims when youre not educated on the subjects. God bless.