What on earth are you talking about that if she were 18 or older, she couldn't have given birth to the messiah.  Not all "scholarly" studies are all that accurate or "scholarly".  Example:  Catholic church teaches Joseph was an old man and Mary a young woman, maybe only 14.  The Catholics taught this because they were determined that Mary remained a virgin all her life.  As though she was too holy to have ever had sex.  So naturally  Joseph was too old to be interested in having sex with his wife and Mary remained "holy" enough to be the "Mother of God".  She was mother to the physical body of Jesus the savior, not the actual Mother of God, He doesn't have a mother.  And scripture clearly teaches that Jesus had younger brothers and sisters.  The Catholic church states that they were actually cousins and that it wasn't unusual for people in those days to call cousins siblings.  Scholars coming up with "facts" that fit their own opinions.