Albert Barnes Commentary 2 Chronicles 36:9

"Jehoiachin was eight years old when he began to reign; and he reigned three months and ten days in Jerusalem: and he did that which was evil in the sight of Jehovah." — 2 Chronicles 36:9 (ASV)

Eight years old - Rather, eighteen (see the marginal reference). Jehoiachin had several wives and (apparently) at least one child (Jeremiah 22:28), when, three months later, he was carried captive to Babylon.