Looking at the verse Isaiah 7:14, when the Lord gave Ahaz a sign:
Therefore the Lord himself will give you a sign. Behold, a young woman shall conceive and bear a son, and shall call his name Immanue
Isaiah 7: 14
Jerome inquires as to the exact meaning of the term, young woman or ‘almah:
“It means: hidden virgin; that is, not only a virgin, but more intensely so, because not all virgins are hidden and withdrawn from the fortuitous glance of men”
Jerome, Adversus Lovinianum I, 32; PL 23, 266.
If you are interested in more quotes on Virgin Mary, you can find them in Mary and the Fathers of the Church on Amazon in both in Kindle and paperback formats.
References:
Gambero, L., 1999. Mary and the Fathers of the Church 1st ed. Translated by Buffer, T., San Francisco: Ignatius Press.