Adam Clarke on 2 Kings 24:8

Jehoiachin was eighteen years old - He is called Jeconiah, 1Chr 3:16, and Coniah, Jer 22:24. In 2Chr 36:9, be is said to be only eight years of age, but this must be a mistake; for we find that, having reigned only three months, he was carried captive to Babylon, and there he had wives; and it is very improbable that a child between eight and nine years of age could have wives; and of such a tender age, it can scarcely be said that, as a king, he did that which was evil in the sight of the Lord. The place in Chronicles must be corrupted.

That he was a grievous offender against God, we learn from Jer 22:24, which the reader may consult; and in the man's punishment, see his crimes.