Manasseh is 12 when he takes over from his father, and reigns for the next 55 years. He's bad, because he rebuilds the temples to Baal, sacrifices his son, and practices sorcery. I wonder what this book would be like if Baal was the protagonist.
What really pisses god off, though, is not the child sacrifice, it's the fact that he puts one of his Baal thotchkes in the temple. In response, god vows to do something so horrible to the Israelites that whosoever heareth of it, both his ears shall tingle (v. 12). More specifically, he says I will wipe Jerusalem as a man wipeth a dish, wiping it, and turning it upside down (v. 13) proving that Israelite men did dishes. For all you women out there having trouble convincing your significant others to do housework, this is one more argument.
We get some other vague examples of how Manasseh is evil, including that he had a lot of people killed, but not who or why or how, so I think we can just chalk that up to exaggeration. Then he dies. 55 years summed up in 17 bible verses. If only the whole book were so tautly plotted.
His son Amon, clearly not the one sacrificed to Baal, although that would be cool, takes over. Amon is also bad. God it's like a broken record, this book. And the next two are the exact same thing with some of the details shifted around. Urgh. Anyway, Amon is killed by his servants, and then his servants are killed by the people, and his son Josiah takes over. Amon was only 22 when he took over the throne, though it's not clear how much time has passed or how old he is at this point.