He was born 2000 years ago not tomorrow lol. Also Dec 25th is not his birthday. He was born in the spring as the shepherds where guarding there sheep. We celebrate his birth in the 25th of Dec. Because Christians were being persecuted and the hid the birth during the festival of lights which was a pagan holiday celebrating the return of the son. Yes I'm sure you get the irony.
Early church fathers discussed dec 25 back in 3rd century. We know what day George Washington was born so why wouldn't the traditional people get it wrong. The shepherds may be an allegorical priestly statement to cover vocational involvement over generations.