It escapes me right now, but I think it was Augustine who
believed the perpetual virginity of Mary could be proven
from Luke. He said that when the angel Gabriel announced to
her that she would conceive a son her question
"how shall this be since I know not man" shows that she had
made a vow of perpetual virginity. The logic being that since
she was already espoused to Joseph the reply would have
made no sense because she was thinking about a conception
through the natural marital act. This of course would
have been done in the normal course of events and thus she could
conceive a son. But she leaves this possibility out when she says
"I know not man" i.e. not now nor or am I planning to later in my marriage.
That is simply another example of the perverse reasoning of men seeking to support an extraBiblical tradition with Scripture. Mary's reply is not, "How shall this be, seeing I WILL NOT know not a man, but that "seeing as I know not a man," as she was not in a consummated marriage. The idea that this means she had taken a vow of perpetual virginity, and that Joseph agreed to this is simply absurd.
Both would be extraordinarily exceptions to the norm, as is the virgins birth, but as abundantly seen when something as this is true among notable characters in Scripture, the virgin birth is clearly stated, as is Christ being sinless, but a unique marriage in which there is consent to leaving but not to cleaving (normally grounds for RC annulment) and the perpetual virginity is not, and what is said best Mary having relations after the Lord's birth.