For one thing, Luke was an historian writing from eyewitness accounts (Luke 1:1-4). One firm historic "marker" found in Acts 24:27 (Festus's appointment as Roman procurator of Judea, which was in AD 59-62) has implications because Acts was written AFTER Luke's Gospel. Thus Luke was written at least before A.D. 63 and possibly before 55-59 since Acts is the second in the series of writings by Luke. This means that the Gospel of Luke was written within 30 years of Jesus' death.
Another point: although Acts is about the events in the first decades after Jesus' ascension into heaven, it does not allude at all to the destruction of the Temple in 70 AD, which was the biggest and most catastrophic thing that had even happened in Jewish history up to that point
If we thought Luke/Acts were written later, it would be unthinkable that these texts, with all their vibrant immediacy, would totally fail to mention that --- it would be like a central European Jew writing recent history in 1955 and failing to mention the Holocaust.
**It is almost certain that Luke/Acts was written before 70 AD.**
Thank you, that’s the number I was looking for this morning, but could not find it.