A: The Legion of Mary is open to all Catholics in good standing with a desire to serve Our Lord Jesus Christ through the intercession of his Blessed Mother Mary. Catholics 18 years of age or older can join adult praesidia whereas Catholics younger than 18 years of age can join junior Legion of Mary praesidia. Catholics who are interested in joining the Legion will start with a three or six month probationary period before taking their Legionary Promise to become Legion members.