Alma 43:16–17

Now, the leader of the Nephites, or the man who had been appointed to be the chief captain over the Nephites — now the chief captain took the command of all the armies of the Nephites—and his name was Moroni; And Moroni took all the command, and the government of their wars. And he was only twenty and five years old when he was appointed chief captain over the armies of the Nephites.

From section: Nephite–Lamanite Face–Off at Jershon

From page: Zarahemla’s Age of War