There is no doubt that Luke knew the birth date of Messiah. There is hardly any way he could have written about the number of months between the annunciation to Elıshaνą and Miryam being five, or the three months Miryam stayed with Elıshaνą, nor make statements that the term days were fulfilled for each of them without knowing when both Yoɦanan and Yeshua were born. Therefore, it follows that he knows when Messiah was born and when his birthday occurs. One can hardly talk with Yeshua’s mother without finding out the date. Any historian doing a biography who neglected this basic piece of information would be negligent.
Now a historian only says “about” such and such an age if he cannot tell exactly. If a historian says “almost” or “nearly” such and such an age and we know he knows the exact answer, then we know that he said “nearly” only to be strictly accurate, meaning that the person was nearing his birth day, but had not quite reached it. Now it so happens that in Greek we may concede that ὡσεὶ may mean both “about” or “nearly, almost.” Since the word may mean both that the writer is guessing or that the writer only saying nearly, we must base our decision on what we know the writer knows. Since Luke has interviewed the people who know we know he knows. So he must mean “nearly 30.” Since Luke knows when his birthday is, if he knows he is nearer to 29 than 30, then he cannot say “nearly 30,” or “about 30,” and if he knows he is 30, then he cannot say “about 30” and mean something like 30 years and 10 months. In fact saying “about 30” with the meaning of “almost 30” which he clearly intended, is much more accurate than just saying he was 29 or 30! The meaning has to be very close to the 30th birth day. This is more accurate than just saying 29 or 30 because those numbers span a whole year without given any information about the part of the year.
Just how closely does Luke use this word? In Luke 8:42 we have
ὅτι θυγάτηρ μονογενὴς ἦν αὐτῷ ὡς ἐτῶν δώδεκα (because he had an only daughter about twelve years). Mark 5:42,
ἦν γὰρ ἐτῶν δώδεκα (because she was twelve years). In Luke 23:44, he says “about (ὡσεὶ) the sixth hour”, but Matthew 27:45 says it was from the sixth hour. In Acts 13:18 Paul says “about (ὡς) forty years,” (recorded by Luke) when we know they were in the wilderness for forty years. The reason is that they crossed the Jordan river just before a full 40 years was reached. They left Egypt on the 15th day of the month in the 1st year, and they crossed the Jordan before the 15th day of the month starting the 41st year. So they were in the wilderness just a bit less than forty full years. Paul is saying “about forty years” simply because it is more precise, and not because he does not know that the correct rounded figure is 40 years to the nearest year.
In Luke 9:28 he says,
about [ὡσεὶ] eight days whereas Matthew and Mark say
after six days. What gives here? Two Sabbaths are in view with six days between them. When Matthew and Mark speak, they mean after the six working days, and therefore the meeting on the mountain was on the Sabbath. They are echoing the language of Exodus 24:16. The sayings about his sufferings referenced in Luke 9:28 happened on a Sabbath eve (Friday Night) or Sabbath day. Luke counts inclusively from Sabbath to Sabbath, but he knows the sayings did not take place exactly at the start of the Sabbath and that the transfiguration did not take place exactly at the end of the Sabbath. So he says “about.” Again the meaning is near to the number stated.
If we suspect that Luke does not know exactly, then “about” may indicate the uncertainty as in Acts 19:7,
about twelve of them in all.
We know that Luke knew how old Messiah was and when his birthday was. This understanding of the text is confirmed by Irenaeus,
For when He came to be baptized, He had not yet completed His thirtieth year, but was beginning to be about thirty years of age. (Against Heresies 2.22.5). Now the 30th year of age is from the 29th birthday to the 30th birthday. Remember the first year of a person’s age is from birth to the 1st birthday. This source is saying he was near to the 30th birthday. Irenaeus was better off to speak the truth here about his impression of the text. He did not know the astronomical implications which the Church does now know, and so they try to explain away the statement as if Luke did not know and was only guessing.
The data in Luke 3:23 and 3:1 narrow the birth date down to a date between September of 3 BC and September of 2 BC. The priestly division data eliminates September of 3 BC leaving only September of 2 BC. This in turn shows that Yoɦanan began his ministry in the spring of AD 29 and Yeshua was baptized nearing the fall of AD 29.