Answer:
we do not know her age expect for the account in Luke…Luke 1:26-27 And in the sixth month the angel Gabriel was sent from God unto a city of Galilee, named Nazareth, To a virgin espoused to a man whose name was Joseph, of the house of David; and the virgin’s name was Mary.
In those days young girls were generally given in marriage somewhere between the ages of 13 and 16 (very young to todays standards) so Mary was most likely somewhere in that age range. Her husband Joseph may have been much older and why we do not read about him after Jesus was a teenager.