@Frank Apisa,
This is copied directly from the catholic encyclopedia.
http://www.newadvent.org/cathen/08504a.htm
"Marriage
It is probably at Nazareth that Joseph betrothed and married her who was to become the Mother of God. When the marriage took place, whether before or after the Incarnation, is no easy matter to settle, and on this point the masters of exegesis have at all times been at variance. Most modern commentators, following the footsteps of St. Thomas, understand that, at the epoch of the Annunciation, the Blessed Virgin was only affianced to Joseph; as St. Thomas notices, this interpretation suits better all the evangelical data.
It will not be without interest to recall here, unreliable though they are, the lengthy stories concerning St. Joseph's marriage contained in the apocryphal writings. When forty years of age, Joseph married a woman called Melcha or Escha by some, Salome by others; they lived forty-nine years together and had six children, two daughters and four sons, the youngest of whom was James (the Less, "the Lord's brother"). A year after his wife's death, as the priests announced through Judea that they wished to find in the tribe of Juda a respectable man to espouse Mary, then twelve to fourteen years of age. Joseph, who was at the time ninety years old, went up to Jerusalem among the candidates; a miracle manifested the choice God had made of Joseph, and two years later the Annunciation took place. These dreams, as St. Jerome styles them, from which many a Christian artist has drawn his inspiration (see, for instance, Raphael's "Espousals of the Virgin"), are void of authority; they nevertheless acquired in the course of ages some popularity; in them some ecclesiastical writers sought the answer to the well-known difficulty arising from the mention in the Gospel of "the Lord's brothers"; from them also popular credulity has, contrary to all probability, as well as to the tradition witnessed by old works of art, retained the belief that St. Joseph was an old man at the time of marriage with the Mother of God. "
Comment:
So the answer to your question is Mary's age at marriage is given in the Apocrypha which most scholars agree were written around the first century.
If you have a problem with this go argue it with the Pope.
"Mary, then twelve to fourteen years of age. Joseph, who was at the time ninety years old,"
Sound like your ideal arranged marriage Frank, never mind the virgin impregnation by God also...
