Albert Barnes Commentary Jeremiah 1:6

"Then said I, Ah, Lord Jehovah! behold, I know not how to speak; for I am a child." — Jeremiah 1:6 (ASV)

There is no resistance on Jeremiah’s part, but he shrinks back alarmed.

I cannot speak—that is, “I cannot prophesy,” I do not have those powers of oratory necessary for success. The prophets of Israel were the national preachers in religious matters and their orators in political matters.

I am a child—this implies nothing very definite about Jeremiah’s age. Still, the long duration of his prophetic mission makes it probable that he was very young when called to the office, as also were Isaiah, Hosea, Zechariah, and others.