c-2. Age of king Jehoiachin: Did this King Begin to Reign at Age 8 or 18?
2 Kings 24:8 says Jehoiachin was 18 years old when he began to rule in Judah, but 2 Chron.36:9 says he was 8 years old at this time. In this matter we learn that Kings is amplified by Chronicles to provide additional information about Jehoiachin's reign.
That this is a typical case of amplification is immediately evident in that Chronicles adds information to the Kings account. Chronicles shows that the 3-month reign of Jehoiachin is a rounded-off figure, the more exact one being 3 months & 10 days. Further, Chronicles adds the detail that the king was taken to Babylon after the end of the year in which he reigned, while Kings makes no mention of this timing.
In regard to the seeming disparity in the king's age when he began to rule, we note that king Joash (or Jehoash) began to rule Judah at age 7 (2 Kings 11:21; 12:1,2 and 2 Chron.24:1), but he was under the tutelage and control of the high priest Jehoiada, who thus was the real ruler for a time. In related fashion, Jehoichin would be the official ruler in Judah at age 18, but Chronicles amplification of Kings reveals that his father let him participate in ruling Judah to prepare him for the future, beginning at age 8. Jehoiachin would likely be an unofficial co-regent for a few years, then an official co-regent receiving formal instruction for several years, finally ruling alone at age 18, after the death of his father. He ruled for just 3 months & 10 days, and was taken to Babylon at the end of the year during which he reigned. We can see that there is a logical explanation for the noting of different ages of Jehoiachin at the start of his reign, the two different Bible books having different aims in this matter.
We should note that Jehoiachin's father, Jehoiakim, was one of the worst of the kings who rebelled against God, seeming even to challenge God to destroy him. He would likely have a constant sense of danger & death that would lead him to prepare his son to succeed him. Indeed, Jehoiakim died in barbaric fashion at age thirty-six.