The date of December 25th probably originated with the ancient "birthday" of the son-god, Mithra, a pagan deity whose religious influence became widespread in the Roman Empire during the first few centuries A.D. Mithra was related to the Semitic sun-god, Shamash, and his worship spread throughout Asia to Europe where he was called Deus Sol Invictus Mithras. Rome was well-known for absorbing the pagan religions and rituals of its widespread empire. As such, Rome converted this pagan legacy to a celebration of the god, Saturn, and the rebirth of the sun god during the winter solstice period. The winter holiday became known as Saturnalia and began the week prior to December 25th. The festival was characterized by gift-giving, feasting, singing and downright debauchery, as the priests of Saturn carried wreaths of evergreen boughs in procession throughout the Roman temples.
Jesus was not born on December 25th. He was 33 1/2 when he died on Nisan 14 which is in April. Do the math.