Albert Barnes Commentary 1 Samuel 13:1

"Saul was [forty] years old when he began to reign; and when he had reigned two years over Israel," — 1 Samuel 13:1 (ASV)

The text of this verse, which is omitted by the Septuagint, is considered corrupt. The numbers indicating Saul’s age when he became king and the duration of his reign are thought to be missing or faulty. Saul may have been about thirty years old at his accession and may have reigned for approximately thirty-two years. This is plausible because we know his grandson Mephibosheth was five years old at Saul’s death (2 Samuel 4:4). Furthermore, these thirty-two years, when added to the seven and a half years between the deaths of Saul and Ishbosheth, account for the forty years assigned to Saul’s dynasty in Acts 13:21.

There is also no clear indication of the time that passed between the events of the previous chapter and those that follow. However, the appearance of Jonathan as a warrior (1 Samuel 13:2), when compared with the earlier mention of Saul as “a young man” (1 Samuel 9:2), implies an interval of at least ten to fifteen years, and possibly more.

The historian’s purpose is to prepare the way for the history of David’s reign. Therefore, he moves directly to the incident in Saul’s reign that led to his rejection by God, as recorded in 1 Samuel 13:13–14.