How old was Mary, daughter of 'Imran, when she conceived our master Jesus, peace be upon him?

There is no legal text that specifies the age of Mary, peace be upon her, when she conceived Jesus, peace be upon him. Al-Qurtubi narrated from Al-Tabari that the Christians claimed she conceived when she was thirteen years old, and that Jesus lived for thirty-two years, and that Mary remained for six years after his ascension, making her age over fifty years. Something similar was narrated from Wahb ibn Munabbih, but its chain of transmission is weak.