The Bible is one of the most important books ever written. It's been translated and edited so many times that its original stories have been compromised over time. For centuries, scholars have been arguing over how the Bible should be interpreted. Otherwise simple words are subjected to intense scrutiny and widely differing interpretations.
Almost the entire Old Testament was written in Hebrew, with some chapters written in Aramaic, Jesus' native tongue. The most common language of the Roman elite was Greek, and so a translation of the Old Testament was undertaken from Hebrew to Greek. The Greek translation of the Old Testament, called the Septuagint, was widely accepted and was even used in many synagogues. The New Testament was actually written in Greek. Shortly after 300 A.D., Christianity was declared the official religion of the Roman empire.
But as we know, every translation is an interpretation. And with translation, there is a chance of misreporting key facts.
The Hebrew version of the Bible uses the word 'almah' to describe Mary. From what I've read (and my disclaimer is that I do not know either Hebrew or Greek to confirm this), the word almah means 'a woman of marriageable age'. Then the Greek translation of the Bible happened, and they used the word 'parthenos', which is a suitable word for 'young woman' and does not neccessarily imply virginity. The Greek term meant a young woman who has come of age, and only later, perhaps due to Christian use, did the term become almost exclusively connected to virginity.
The reason why some scholars believe that parthenos was meant to mean 'young woman' to describe Mary is because the word is actually used 5 times in Gen.24 to describe Rebekah, a young girl who marries an unknown relative, Isaac, and later gives birth to twins, one of which was Jacob. Also, the Hebrew word for 'virgin' is 'bethulah' and cannot be found anywhere in the original Hebrew text. This brings one to believe that the original writer did not intend for it to be read as 'virgin', but as 'young girl'.
The English reader is given a translation of a text from another language which meant something different in the other language.
Was this a mistake or purposeful?
The Bible may be divinely inspired, but there are human fingerprints all over it. Combined with a misogynist religious culture, you begin to realize that Jesus must have been born of a virgin. Imagine Mary as just an average, young girl. How much would that change things? On the other hand, there are those that believe the word was strategically chosen, the end result being that Mary was held above other women and led a holier existence.
It's at least something to think about.