Manasseh was twelve years old when he became king, and he reigned fifty-five years in Jerusalem. His mother’s name was Hephzibah. 2 Kings 21:1

I have no problems with twelve-year-olds but I would not want one as president.
Manasseh’s dad was Hezekiah, who took away the foreign gods and basically did good in the sight of the Lord.
Manasseh filled Jerusalem and the Temple with foreign gods and idols. He sacrificed a son and allowed fortune-tellers and mediums to live.
Legend says he executed the prophet Isaiah by sawing him in two.

Moreover, Manasseh shed very much innocent blood, till he had filled Jerusalem from one end to another, besides his sin by which he made Judah sin, in doing evil in the sight of the Lord. 2 Kings 21:16

Because of his sin, the Assyrian army attacked Jerusalem and captures him, sending him to Babylon in chains.
It’s not the end of the story. You find a bright note on the life of Manasseh in 2 Chron 33:12-13: Now when he was in affliction, he implored the Lord his God, and humbled himself greatly before the God of his fathers, and prayed to Him; and He received his entreaty, heard his supplication, and brought him back to Jerusalem into his kingdom. Then Manasseh knew that the Lord was God.

From that point forward Manasseh lived for the Lord God, undoing many of the evils of his reign.
I’m glad Manasseh had this turnaround in his life, yet some things he could not undo, like all the deaths under his reign, including Isaiah.

Perhaps you have things in your life you cannot undo too! Take heart in what God says to you – if we walk in the light as He is in the light, we have fellowship with one another, and the blood of Jesus Christ His Son cleanses us from all sin. 1 John 1:7

There is restoration through Christ.