What does Acts 12:6 mean?

Herod Agrippa I is the grandson of Herod the Great (Matthew 2:1). In his younger years in Rome, he made a habit of getting into trouble and relying on his wife to bail him out. When his friend Caligula became Caesar, Agrippa was given rule of the tetrarchy of his uncle Philip, northeast of Galilee. In time, his political machinations proved effective, and he now controls Galilee, Samaria, Judea, and Perea across the Jordan River.

In addition, he has earned the favor of the Sanhedrin by showing a modest but effective respect for Judaism. For some unspecified reason, he has arrested and beheaded the apostle James. When he realizes the move has made him even more favorable to the Sanhedrin, he arrests Peter but wants to wait until after the Feast of Unleavened Bread before he executes him (Acts 12:1–5).

Peter has been arrested twice before, but only by Sanhedrin guards who have no authority to execute a prisoner (Acts 4:1–22; 5:17–40; John 18:31). Now, he has been arrested by Roman soldiers. He is probably being kept in the Fortress Antonia, the guardhouse on the northwest corner of the Temple Mount. Jesus has told him that he will die by crucifixion (John 21:18–19), so he has plenty of reasons to be nervous.

However, Jesus also told Peter he would be "old" when he died. Agrippa reigned over Judea from AD 41 until his death in AD 44—so this is no later than fourteen years after Jesus' ascension. Peter knows his ministry isn't finished, but even if it were, he would face death on behalf of Jesus. It's noteworthy that at this moment, he's fast asleep. In fact, tradition states that when the Romans finally do sentence him to crucifixion, he demands to be hung upside-down as he has no right to die like his Savior.