ειπεν δε μαριαμ προς τον αγγελον πως εσται τουτο -επει- ανδρα ου γινωσκω
Luke 1:34 - TR (Stephens 1550, Beza 1598, Elzevir 1624 and Scrivener 1894 are all identical.)
Then said Mary unto the angel, How shall this be, seeing I know not a man? KJV
The Greek conjunction ἐπεί epei (see Strong 1893) cannot be manipulated into meaning something with regard to a time sequence in the future. The force of the word is 'because' or ' for the reason that'. Note that the KJV quite correctly renders the conjunction as a present participle.
"How shall I bear a child in my situation of not (presently) knowing a man ?"
. . . is all that can possibly be construed from the Greek wording .
[ There is a disputed translation of Luke 7:1 (see interlinear) where epei is rendered 'and when' but the meaning has the force of 'and for the reason that he had completed ...'. It is not a future consequence but, here in Luke 7:1, epei conveys a decision made upon a completed situation. ]
As to Mary's words in Luke 1:34, The Douay-Rheims also correctly renders the conjunction (from the Latin Vulgate) using the very apposite English conjunction 'because':
And Mary said to the angel: How shall this be done, because I know not man?
However the D-R then mis-translates ανδρα (from aner - an identifiable man) and renders it as though it was ἄνθρωπος (anthropos - humanity). This may be a fault of the Latin-from-Greek translation of the Vulgate or it may be a fault of the English-from-Latin translation thereafter.
'Know not man' is quite inappropriate, here. It should be 'know not a man', meaning a particular man. Only an impossibly travelled harlot would know anthropos. Broadening the meaning of 'a man' to 'mankind' in no way strengthens an argument for perpetual virginity.
This attempt to extend Mary's utterance in perpetuity has resulted in very inappropriate English words being put into her holy lips with regard to humanity.
Mary was already espoused to Joseph before Gabriel appeared to her (see Luke 1:27 - ... to a virgin espoused to a man ... ). Hardly the action of a woman who intends, in perpetuity, to remain a virgin. But, having not (yet) come together (Matthew 1:18), she did not (at that stage) know a man.
What is much more relevant regarding the certainty of the situation is Matthew's wording in Matthew 1:24, 25 :
Then Joseph being raised from sleep did as the angel of the Lord had bidden him, and took unto him his wife: And knew her not till she had brought forth her firstborn son: and he called his name JESUS. [KJV]
Had Matthew wished to convey - without a trace of ambiguity - that Mary had remained a virgin thereafter, Matthew would have stopped writing after 'knew her not'.
... and took unto him his wife and knew her not [Full Stop]
Thereafter he would have made a new sentence regarding the name of Jesus.
But he does not do that, he continues :
... until she had brought forth the son of her (in literal) ...