1 Kings 11:4

For it came to pass, when Solomon was old, that his wives turned away his heart after other gods: and his heart was not perfect with the LORD his God, as was the heart of David his father.

When Solomon was old. He could not have been more than 50. But his love of splendour was intense; and a long course of voluptuous indulgence had so far weakened the energy of his will, that, in opposition, it must be supposed, to his better judgment, he succumbed to the domination of the senses.

His wives turned away his heart after other gods. Some, considering the lapse of Solomon into idolatry as a thing incredible, regard him as merely humouring his wives in the practice of their superstition, and, in countenancing their respective rites by his presence, as giving only an outward homage, a sensible worship, in which neither his understanding nor his heart were engaged, but from his fondness for a sensuous ritual, dazzled and took strong hold of his imagination. The apology only makes matters worse, as it implies an adding of hypocrisy and contempt of God to an open breach of His law. There seems no possibility of explaining the language of the sacred historian, but as intimating that Solomon became an actual and open idolater - [to go "after other gods" (1 Kings 11:5) is the usual formula for lapsing into idolatry (Deuteronomy 8:19; Deuteronomy 11:28; Deuteronomy 13:3; Judges 2:12; Jeremiah 35:15)] - worshipping images of wood or stone in sight of the very temple which in early life he had erected to the true God. Hence, that part of Olivet was called the high place of Tophet (Jeremiah 7:30); and the hill is still known as the Mount of Offence, or the Mount of Corruption (2 Kings 23:13).