"12-Year-Old Jesus Argument" for Mary's Perpetual Virginity

Opponents of Mary's perpetual virginity put forth several speculative biblical arguments from silence. We Catholics have some of those, too (two can play at that game). Here's one of the best ones:

Luke 2:41-42 (RSV) Now his parents went to Jerusalem every year at the feast of the Passover. [42] And when he was twelve years old, they went up according to custom;

We don’t see a word about any other children, who certainly would have gone with Joseph and Mary to observe the Passover in Jerusalem. This means that if Mary had other children, there was at least a twelve-year gap, which is hardly likely, feasible, or plausible in those days, with a young married woman (who already bore one child) of approximately 16-28 years of age. Generally (as was the case up until very recently), wives had children one after another.

Luke 2:48 records Mary's words to Jesus: "your father and I have been looking for you anxiously." Now, if several other children (Jesus' supposed siblings) had gone along on the pilgrimage, certainly they would have been looking for Him, too. They would have been sent out in all directions. So wouldn't Mary have likely said something like: "your father and I and your brothers and sisters have been looking for you anxiously"? But the text shows no awareness whatsoever that there are any sons and daughters of Joseph and Mary besides Jesus.

Then afterwards, the Bible states that “he went down with them and came to Nazareth” (2:51). If the other supposed siblings had also been there, the text would have presumably read something like, “he went down with his brothers and sisters and parents and came to Nazareth”. But it didn’t, and we submit that it didn’t because (it seems most plausible to me) those siblings didn’t exist.

If indeed Jesus had literal brothers and sisters (siblings), it also has to be accounted for, why (assuming the above argumentation is correct) would there be a twelve-year gap in childbearing, with Mary and Joseph then having many more children (if "brethren" in the Bible is taken to always mean "siblings": which is demonstrably not the case)? This is not plausible. On a Reddit AskHistorians page (“What was the average number of children a Christian family had around 0-100 A.D.?”), one of the historians, Jason Caspian, stated that “it's safe to say a few things demographics wise. On average, typical Jewish peasant who lived an agrarian type of life-style could typically have up to 4-8 children, . . .” It follows that it is exceedingly unlikely that there would be this (at least) twelve year gap in children being born, especially since in this erroneous thinking, there were at the very least six siblings of Jesus ("his brothers James and Joseph and Simon and Judas": Mt 13:55, and "his sisters": Mt 13:56).

There are many other good, strictly biblical arguments for these "brothers" and "sisters" being cousins or step-siblings (beyond my purview at present, but I have written many arfticles about that on my web page devoted to the Blessed Virgin Mary). They go right along with the above arguments, and it becomes a strong argument from cumulative effect. But here is but one of many of such arguments:

Jesus’ “brethren” in Scripture are never called the children of Mary, and Mary is never called their mother, as in the case of Jesus:

John 2:1 On the third day there was a marriage at Cana in Galilee, and the mother of Jesus was there;

John 19:25 . . . standing by the cross of Jesus were his mother, and his mother’s sister, Mary the wife of Clopas, and Mary Mag’dalene.

In at least two instances, these “brothers” were mentioned but Mary wasn’t called their mother; only Jesus‘ mother:

Acts 1:14 All these with one accord devoted themselves to prayer, together with the women and Mary the mother of Jesus, and with his brothers.

Mark 6:3 Is not this the carpenter, the son of Mary and brother of James and Joses and Judas and Simon, and are not his sisters here with us?” . . .

Doesn’t it stand to reason and isn’t it common sense that if these “brothers” were indeed the siblings of Jesus, that Acts 1:14 would read, instead: “Mary the mother of Jesus and his brothers”? Then we wouldn’t be having this dispute; it would have been so clear and undeniable. A similar argument could be made for Mark 6:3. But instead, we have Jesus only being called “the son of Mary” there, while “son of Mary” referring to someone besides Jesus, or the phrase “sons of Mary” never appear in Holy Scripture.