According to the author of the book, Zedekiah became a king when he was 21 years old and ruled for 11 years in a place called Jerusalem. His mom was named Hamutal, and her dad was Jeremiah from a town called Libnah.
2 Kings 24:18: Zedekiah [was] twenty and one years old when he began to reign, and he reigned eleven years in Jerusalem. And his mother's name [was] Hamutal, the daughter of Jeremiah of Libnah.
States the same age and reign period for Zedekiah as 2 Kings 24:18, so no direct contradiction here.
2 Chronicles 36:11: Zedekiah [was] one and twenty years old when he began to reign, and reigned eleven years in Jerusalem.