The problem is that this would be a major departure from Jewish tradition that held that you were to find your daughter a husband that was of her youth rather then marrying her off to one of your old cronies.
It was considered a shameful thing to marry a young virgin to an elderly man.
>> It was considered a shameful thing to marry a young virgin to an elderly man. <<
Actually, that notion is included in the Greek stories about the marriage of Mary to Joseph. Here, I’m citing the most common elements of the stories, which have some variations among versions:
They say Mary’s parents had conceived of her in their old age, much like Elizabeth and Zecharias. When she became pregnant as her father had prophecied, everyone presumed that a great prophet was to be born, and her parents, expecting a boy, pledged that the child shall be raised in the Temple. When a girl was born, they devised a test that they were certain she would fail: she would choose between her parents or the Temple.
For several years, she was allowed to stay in Temple, but when she came of age to menstruate, Jewish law forbid her from being in the Temple. (Anna was allowed because she was passed the age of menstruation.) Against her desires to remain ever-virgin, the Temple elders assembled all the eligible youth and released a dove; whoever the dove chose would be her husband. The dove left the area, and instead landed upon Joseph. The Temple elders were aghast, but the staff Joseph held in his hand bloomed as foretold of the staff of Jesse’s stem.
This, then, is the particular shame why the bible had Joseph plotting to send Mary off in secret, whereas “jumping the gun” while already betrothed would’ve been socially tolerated by many: He was an old man married to a young virgin! The shame of not being able to keep it in his pants (er, tunic?) was unbearable!
But also note that when Mary returned to the Temple, Simon and Anna at the Temple knew immediately that Mary’s child represented the fulfillment of the prophesy that a Virgin would give birth: they knew she was a Virgin! Yes, their correct interpretation of this was a prophecy inspired by the Holy Spirit, but no, prophesy isn’t fortune-telling; it’s correctly interpreting what is unbelievable to those unaided by grace.