Ambrose of Milan — as excerpted in the Catena Aurea on Luke 1:23-25

“What reason then for concealment, except shame? For there are certain allowed times in wedlock, when it is becoming to attend to the begetting of children; while the years thrive, while there is hope of child-bearing. But when in good time old age has come on, and the period of life is more fitted for governing children, than begetting them, it is a shame to bear about the signs of pregnancy, however lawful. It is a shame to be laden with the burden of another age, and for the womb to swell with the fruit of not one’s own time of life. It was a shame then to her on account of her age; and hence we may understand the reason why they did not at this time come together, for surely she who blushed not at their coming together in their old age, would not blush at her child-bearing; and yet she blushes at the parental burden, while she yet is unconscious of the religious mystery. But she who hid herself because she had conceived a son, began to glory that she carried in her womb a prophet.”