Which Old Testament Prophet said, "Ah, Soveriegn Lord, I do not know how to speak; I am only a child."
It was Jeremiah in Jeremiah 1:4-8. God didn't accept the excuse and put him to work anyway!
Click here to read about Jeremiah and the book that bears his name.
Rembrandt's painting of Jeremiah (above) shows him lamenting the destruction of Jerusalem by the Babylonian Empire.