The Bible does not say how old Mary was. Most of the posts below are speculation ba<x>sed on traditions thought up by men.
About 12. Before feminism 12-14 was pretty much the standard age for young women to be getting married and getting on with their lives. Now we pretend that they are "adolescents" a fabricated 20th century fiction, or even "children" which is obviously wrong.
Children are not yet past biolgoical puberty. You are a blind fool who refuses to see what is right in front of him.
Twist....twist....twist.... All it takes is a right click: Child --> " a young person especially between infancy and youth"
She was about 12, standard age for marriage at that time. Thirteen when Jesus was born.<br />
If she was married according to tradition she was probably married to joseph around 16.