Matthew Poole's Concise Commentary
2 Kings 18:2
Twenty and five years old was he when he began to reign. How is this credible? For then Ahaz, who lived but six and thirty years, 2 Kings 16:2, must beget Hezekiah at the eleventh year of his age. Answ.
1. There are some like instances mentioned by credible authors; which these very men will not deny, who are so ready to quarrel with the Holy Scriptures for such matters.
2. This being the confessed custom of sacred and other writers, in the numbering of years, sometimes to omit, and sometimes to add, those which are imperfect or unfinished; and so Ahaz might be near one and twenty years old when he began to reign, and near seventeen years older when he died. And on the other side, Hezekiah, when he began to reign, might be only four and twenty years old complete, and but entered into his five and twentieth year. And thus Ahaz might be between thirteen and fourteen years old when he got Hezekiah; which is not at all strange, especially in that nation, to which God had promised a singular degree of fruitfulness, and in that house of David, to which God had made so many and such great promises.
3. It is not certain that Ahaz lived only thirty six years; for those sixteen years which he reigned, 2 Kings 17:2, may be computed, not from the first beginning of his reign, when he reigned with his father, (of which See Poole on "2 Kings 15:30",) which was at the twentieth year of his age, but from the beginning of his reign alone.
4. Some affirm that Hezekiah was not the natural, but only the legal son and successor of Ahaz; for the name of son is given in Scripture to such persons; as 1 Chronicles 3:16, compared with 2 Kings 24:17 Matthew 1:12, compared with Jeremiah 22:30; and to adopted sons, Acts 7:21 Hebrews 11:24; and to sons-in-law, 1 Samuel 24:16, 1 Samuel 26:17 Luke 3:23. Any of these solutions are far more credible to any man of common prudence, than that these sacred books, whose Divine original hath been so fully evidenced both by God and men, are but the fictions and contrivances of a base impostor. And if none of these solutions were sufficient, it is absurd to conclude that a true resolution cannot be found because it is not yet found; because it is manifest, that many difficulties, both in Scripture and in the arts, which were formerly judged insoluble, have been cleared in later times; and therefore we may justly expect the resolution of other difficulties, which may be thought not yet fully explained. Abi, or Abijah, 2 Chronicles 29:1.