well, ”his girl is virgin” should be right too. In Romanian, ”fată mare” is the most common expression for ”virgin”, generally with negative connotation. ”Ea este fată mare” has no other meaning (except in rare cases). :)
You can tell to a 3 years old girl ready to cry ”nu plânge, tu ești fată mare acum, nu-i așa?” and that would mean without doubt ”don't cry, you are a big girl now, aren't you?”, but if you ask a 15 years old girl the same question, it will mean without doubt that you are hinting that she is not virgin anymore (and it is indeed rude).
Alright, so “fată mare” is used to mean „virgin“ but here we have „fata … este mare.“ I have never heard the predicative adjective „mare“ mean „virgin,“ even if the subject is “fată.” For your version, wouldn't you need to say „fata sa este o fată mare?“
Imho the most part of the „virgin“ meaning in Romanian lies in “fată,“ not in „mare:” She is big and still a girl (not a woman). So I think „mare“ alone never means virgin. Note that in your sample phrase you say „tu ești fată mare acum,“ not „tu ești mare acum.“
No sexism or offence of any kind intended (needless to say, I hope).