More Biblical Timeline
Let's start with the account of Luke in the 3rd chapter, verses 1 through 4:
1 Now in the fifteenth year of the reign of Tiberius Caesar, Pontius Pilate being governor of Judea, Herod being tetrarch of Galilee, his brother Philip tetrarch of Iturea and the region of Trachonitis, and Lysanias tetrarch of Abilene,
2 while Annas and Caiaphas were high priests, the word of God came to John the son of Zacharias in the wilderness.
3 And he went into all the region around the Jordan, preaching a baptism of repentance for the remission of sins,
4 as it is written in the book of the words of Isaiah the prophet, saying: “The voice of one crying in the wilderness: Prepare the way of the LORD; Make His paths straight."
According to Ancient History Encyclopedia, Tiberius Caesar reigned from 9-18-14 AD through 3-16-37 AD. Starting with 14 AD as the first year, the fifteenth year would be 28 AD.
As shown earlier, the birth year of John the Baptist and Jesus is 3 BC. So in spring of 28 AD, John would be 30 years old. Jesus was born in the early fall and John was born about 6 months earlier, as indicated in Luke 1:24-38:
24 Now after those days his wife Elizabeth conceived; and she hid herself five months, saying,
25 “Thus the Lord has dealt with me, in the days when He looked on me, to take away my reproach among people.”
26 Now in the sixth month the angel Gabriel was sent by God to a city of Galilee named Nazareth,
27 to a virgin betrothed to a man whose name was Joseph, of the house of David. The virgin’s name was Mary.
28 And having come in, the angel said to her, “Rejoice, highly favored one, the Lord is with you; blessed are you among women!”
29 But when she saw him, she was troubled at his saying, and considered what manner of greeting this was.
30 Then the angel said to her, “Do not be afraid, Mary, for you have found favor with God.
31 “And behold, you will conceive in your womb and bring forth a Son, and shall call His name JESUS.
32 “He will be great, and will be called the Son of the Highest; and the Lord God will give Him the throne of His father David.
33 “And He will reign over the house of Jacob forever, and of His kingdom there will be no end.”
34 Then Mary said to the angel, “How can this be, since I do not know a man?”
35 And the angel answered and said to her, “The Holy Spirit will come upon you, and the power of the Highest will overshadow you; therefore, also, that Holy One who is to be born will be called the Son of God.
36 “Now indeed, Elizabeth your relative has also conceived a son in her old age; and this is now the sixth month for her who was called barren.
37 “For with God nothing will be impossible.”
38 Then Mary said, “Behold the maidservant of the Lord! Let it be to me according to your word.” And the angel departed from her.
Shortly after John started his ministry, baptizing multitudes of people in the Jordan river, he then baptized Jesus who was about 30 years old at that time, as recorded by Luke in the 3rd chapter verses 21 through 23:
21 When all the people were baptized, it came to pass that Jesus also was baptized; and while He prayed, the heaven was opened.
22 And the Holy Spirit descended in bodily form like a dove upon Him, and a voice came from heaven which said, “You are My beloved Son; in You I am well pleased.”
23 Now Jesus Himself began His ministry at about thirty years of age, being (as was supposed the son of Joseph), the grandson of Heli,
(Note: The words “his ministry” are not in the Greek text, but are implied. Direct objects were frequently omitted in Greek when clear from the context, but must be supplied for the contemporary English reader. (New English Translation Notes)
Luke's above account further proves that Jesus was born in 3 BC.