I agree a lot of it is cultural in that western modern teens are nowhere near mature enough to consent or handle such responsibilities. I find it hard to believe a twelve year old at any time could - but as Mary was 12, it just seems to me that the Church does not consider it wrong. Someone pointed out that society changed (lifespan etc) and I totally agree…but the Church teaches morality does not change based on society necessity…so I mean it’s not like the Church found it moral then and not now. I of course believe a twelve year old should not have sex wth a 30 year old, but obviously this was at one time considered normal, and is accepted by the Church (and if you believe the story of Mary, apparently by God or why would he not have had Jesus born to an older woman? Not lke 40, but at least late teens)
In actuality, I do not believe I have ever heard of anywhere that the “Catholic Church” has assigned an age to Mary. It has been presumed that she was at or beyond the age of marriage eligibility according to Jewish Laws in place at that time.
oce.catholic.com/index.php?title=Mary%2C_The_Blessed_Virgin
**Jewish maidens were considered marriageable at the age of twelve years and six months, though the actual age of the bride varied with circumstances. The marriage was preceded by the betrothal, after which the bride legally belonged to the bridegroom, though she did not live with him till about a year later, when the marriage used to be celebrated. All this well agrees with the language of the Evangelists. St. Luke (i, 27) calls Mary “a virgin espoused to a man whose name was Joseph”; St. Matthew (i, 18) says, “when as his mother Mary was espoused to Joseph, before they came together, she was found with child, of the Holy Ghost”. As we know of no brother of Mary, we must suppose that she was an heiress, and was obliged by the law of Num., xxxvi, 6, to marry a member of her tribe. The Law itself prohibited marriage within certain degrees of relationship, so that the marriage of even an heiress was left more or less to choice. According to Jewish custom, the union between Joseph and Mary had to be arranged by the parents of St. Joseph. One might ask why Mary consented to her betrothal, though she was bound by her vow of virginity. As she had obeyed God’s inspiration in making her vow, so she obeyed God’s inspiration in becoming the affianced bride of Joseph. Besides, it would have been singular among the Jews to refuse betrothal or marriage; for all the Jewish maidens aspired after marriage as the accomplishment of a natural duty. Mary trusted the Divine guidance implicitly, and thus was certain that her vow would be kept even in her married state. **
Further:
newadvent.org/cathen/01541c.htm
The opinion that Joseph at the time of the Annunciation was an aged widower* and Mary twelve or fifteen years of age,** is founded only upon apocryphal documents. The local tradition of Nazareth pretends that the angel met Mary and greeted her at the fountain, and when she fled from him in fear, he followed her into the house and there continued his message. (Buhl, Geogr. v. Palaest., 1896.) The year and day of the Annunciation cannot be determined as long as new material does not throw more light on the subject. The present date of the feast (25 March) depends upon the date of the older feast of Christmas.*
No-one really knows… though I have seen where it has been said that Mary was born in the year 20 BC, which would then make her 20 or 21 when Christ was born…
