Virgin Mary, Giovanni Battista Salvi da Sassoferrato
If you were to ask me how the Most Holy Virgin spent the time of Her youth, I would answer that that is known to God Himself and the Archangel Gabriel, Her constant guardian. — St. Jerome
The quote above is found on tons of Eastern Orthodox sites, all within the same homily that has been copied from place to place — and with no attribution for St. Jerome's quote. So it is probably too apt to be something St. Jerome actually said. However, it does reflect my feelings about knowing details about the Virgin Mary's childhood which I discovered "everyone knows" after I became Catholic. The tale of her miraculous birth, "presentation" to the Temple, and similar details come from a 2nd century apocryphal book which has been rejected by the Church, The Protoevangelium of James.
Today's feast is associated with an event from the Protoevangelium that Mary's parents brought her as a child they brought her to the Temple in Jerusalem to consecrate her to God. Later versions say that Mary was taken to the Temple to live at around the age of three to fulfill a vow.
Did that happen? Who knows? Despite that, there is a good reason to care about this feast day.
St. Luke is notably diligent in examining all the sources that can offer personal information concerning the people he describes. In the case of Mary's childhood, however, he omits any mention of specific facts. Our Lady most probably never mentioned anything about her earliest years, since there would be very little in them of extraordinary interest ...
The feast we celebrate today does not have its origin in the Gospel, but in ancient tradition. The Church, however, does not accept the fictitious narrative that supposes Our Lady to have lived in the Temple under a vow of virginity from the time she was a young maiden. But the essential basis of today's feast is firm — the personal oblation that the Blessed Mother made to the Lord during her early youth. She was moved by the Holy Spirit to consecrate her life to God, who filled her with grace from the first moment of her conception. Mary's complete dedication was efficacious, and continued to grow as her life went on. Her example moves us not to withhold anything in our own life of dedication to the Lord. ...
Our Lady was moved by a special grace of the Holy Spirit to commit her entire life to God. Perhaps she made the decision just as she reached the age of reason, a mile-stone in any life and a moment that must have been particularly significant for a person as full of grace as Mary was. Maybe the Blessed Virgin naever mae a formal declaration of her commitment to God, but was simply accustomed from the beginning of her life to living her dedication in a natural way. ...
Today is a good opportunity — as every day is — to renew our own dedication to the Lord in the midst of our daily duties, in the specific situation in which God has placed us.
Francis Fernandez, In Conversation with God, Special Feasts: July-December