Imperator Caesar Divi Filius Augustus ruled the Roman Empire from 27 BC to 14 AD.
Luke 2:1-5
1 And it came to pass in those days, that there went out a decree from Caesar Augustus, that all the world should be taxed.
2(And this taxing was first made when Cyrenius was governor of Syria.)
3 And all went to be taxed, every one into his own city.
4 And Joseph also went up from Galilee, out of the city of Nazareth, into Judaea, unto the city of David, which is called Bethlehem; (because he was of the house and lineage of David
5 To be taxed with Mary his espoused wife, being great with child.
Yet August did not always hold the title Divi filius during his reign, so A.D. might signify the period when Imperator Caesar Divi Filius Augustus had was given the title as the Son of God. Yet they say that Cyrenius wasn't governor of Syria until 6 A.D.
So if Jesus was taken by the chief priests beyond Jordan to be baptised in the fifteenth year of Tiberius Caesar Divi Augusti filius Augustus according to Luke 1.
Now in the fifteenth year of the reign of Tiberius Caesar, Pontius Pilate being governor of Judaea, and Herod being tetrarch of Galilee, and his brother Philip tetrarch of Ituraea and of the region of Trachonitis, and Lysanias the tetrarch of Abilene,
Luke 1:1
Thus if Augustus ruled until 14. A.D. and Tiberius had been ruling for 15 years then it would have been in 29 A.D. that the chief priests took him beyond Jordan to be baptized of John.
22 And the Holy Ghost descended in a bodily shape like a dove upon him, and a voice came from heaven, which said, Thou art my beloved Son; in thee I am well pleased.
23 And Jesus himself began to be about thirty years of age, being (as was supposed) the son of Joseph, which was the son of Heli,
Luke 3:22-23
However, it would seem more likely that in the first year of Augustus reign over the Roman Empire that he would decreed that the world would be taxed which would have meant that the in the 15 year of Tiberius rule then Jesus would have been 46 years old at the time of his baptism. And thus if 3 1/2 years till his public crucifixion that could explain why in John 8:57 "then said the Jews unto him, Thou art not yet fifty years old, and hast thou seen Abraham?"