Mary and Zechariah

The Gospel of Luke reports that the angel Gabriel announced miraculous conceptions to two different people: first to Zechariah, a priest of the Temple in Jerusalem; then to Mary, a “virgin betrothed”.

One of the curious differences in the stories is reflected in the following:
Zechariah said to the angel, “How shall I know this? For I am an old man, and my wife is advanced in years.” And the angel said to him in reply, “I am Gabriel, who stand before God. I was sent to speak to you and to announce to you this good news. But now you will be speechless and unable to talk until the day these things take place, because you did not believe my words, which will be fulfilled at their proper time.”

Mary said to the angel, “How can this be, since I have no relations with a man?” And the angel said to her in reply, “The holy Spirit will come upon you, and the power of the Most High will overshadow you. Therefore the child to be born will be called holy, the Son of God. And behold, Elizabeth, your relative, has also conceived* a son in her old age, and this is the sixth month for her who was called barren; for nothing will be impossible for God.”
A rather stark disparity, no? Both ask how it is possible, since it seems impossible. Both receive answers, but only one is silenced for nine months.As a half-Italian, I suspect the real reason is that God is more favorably inclined to His Mother.

I’ve read quite a few reflections on this disparity: why is Zechariah muted, and Mary not? Most answers fail to convince me. For instance, one explanation has it that the slightly different wording makes a world of difference:
Κατὰ τί γνώσομαι τοῦτο (Zechariah) / Πῶς ἔσται τοῦτο (Mary)
I know only enough Greek to recognize a few words, and they’re definitely different, so I guess it’s possible, but…

I don’t remember seeing this possibility: Perhaps someone has given this potential explanation; perhaps I’ve even read it, and forgotten. I don’t claim originality; I just wonder.