It has absolutely nothing to do with the Julian calendar. The date on the civil calendar for Julian December 25 is January 7, not 6! There is further evidence, that being that where the Old Calendar is retained in the Armenian Church (in the Holy Land, Georgia, and Russia), the celebration is on January 19th! The reality is that originally the Nativity of Christ was commemorated on Theophany throughout the East, and the Armenian Church never departed from this practice like everyone else.