1 Chronicles 3:15 says Jehoiakim was born 2nd, Zedekiah was born 3rd, and Shallum [Jehoahaz] was born 4th.
Jehoahaz was 23 years old when he became king, and Jehoiakim was 25 years old when he became king 3 months later. So how is it that 11 years later Zedekiah is only 21 years old when he becomes king? Shouldn't he be 35 years old according to 1 Chron. 3:15?