When did "virgo" gain its sexual meaning?

Question

The primary meaning I associate with virgo, virginis is "young woman", perhaps a bit older than a puella but not yet a mulier.

However, the descendants of this word (in English and the Romance languages) tend to have a specifically sexual meaning: a "virgin" is someone (of either gender) who's never had sex with anyone. And L&S mention the word being used in Ecclesiastical Latin for various church fathers, who certainly were not young women.

So—when did this shift take place? In other words, until what point in history could I use virgo to mean a young woman without sexual implications? And did this differ at all in Classical versus Vulgar Latin?

Answer 1

As far as I can see, your basic premise is doubtful, inasmuch as classical sources appear to have defined virgo in the same way as has been done down to modern times. Certainly, the word was then applied to girls, young women and various males, but generally implying maidenhood, sc. an absence of sexual experience.

There are plenty of examples. Cicero has a particularly striking demonstration, quinta Pallantis, quae patrem dicitur interemisse virginitatem suam violare conantem, cui pinnarum talaria adfigunt, (de Natura Deorum iii, 59); Pliny Maior, xxviii, passim, has a good deal to say on the subject; and of course the Vestal Virgins were young women who might be severely punished for sexual transgression, chosen before puberty and not discharged from their vows until the age of forty.

Answer 2

A girl (not woman. Not "young woman", that's a modern concepts), in most of the ancient cultures (I don't talk about modern cultures, that's different), was a woman who were not married.

When a girl was married, she became a woman (it wasn't a matter of age, but a matter of status: being married = to be a woman. Quite different with the nubility.)

And as a non-married woman was supposed to be virgin, both "girl" and "virgin" was perfect synonym (at least in the concept, not always in reality, but it's another thing...)

Of course, it's not true in some societies where the religion didn't prevent to have out of marriage relationship, or where it was not advisable to marry a virgin.

But it's the case in the Hebrew, Greek and Roman societies, for instance.

For the Hebrew society, you can refer yourself to the Old Testament.
For the Greek society, it's mentioned in many texts, for instance, on Wikipedia, they say:

A gamos, a marriage ceremony, was conducted. It started with a sacrifice, proteleia, (premarital), which was for the gods to bless the two being wed. Then the future wife would cut her hair signifying her previous virginity.

For the Roman society, many texts also, for instance:

Celibacy and Fertility
In ancient Rome, all women had to remain celibate before marriage. Their fathers typically arranged their marriage when they were very young, and they were never given the option to date or fall in love. If a man was caught having sex out of wedlock, it was fine, but for a woman, it would be a death sentence. The age of consent was 12 for girls and 14 for boys, but many parents waited for their daughters to have an education before getting married, even if they had been promised to a man for years. They typically got married in their late teens to early 20’s.

https://historycollection.co/10-details-from-the-daily-life-of-vestal-young-women-in-ancient-rome/

Another argument, Minerva was called the "virgo minerva", and it has been described that the meaning was "the chaste Minerva".

So, yes a girl, and a virgin means the same, it's not different from medieval European literature.