Albert Barnes Commentary 1 Kings 3:14

"And if thou wilt walk in my ways, to keep my statutes and my commandments, as thy father David did walk, then I will lengthen thy days." — 1 Kings 3:14 (ASV)

I will lengthen your days — The promise here was only conditional. As the condition was not observed (1 Kings 11:1–8), the right to the promise was forfeited, and it was not fulfilled. Solomon can scarcely have been more than fifty-nine or sixty at his death.