Josh found his notes on the dating of Christmas and the farthest date of December 25th he could find referenced was in 200 A.D. from Hippolytus of Rome

“23.3. For the first advent of our Lord in the flesh, when he was born in Bethlehem, was December 25th,3 Wednesday,4 while Augustus was in his forty-second year, but from Adam, five thousand and five hundred years. He suffered in the thirty-third year, March 25th,5 Friday,6 the eighteenth year of Tiberius Caesar, while Rufus and Roubellion were Consuls.” Hippolytus of Rome 202-211 A.D.