Jeremiah – The Young Prophet 

Now the word of the Lord came to me saying, “Before I formed you in the womb I knew you, and before you were born I consecrated you; I have appointed you a prophet to the nations.” Then I said, “Alas, Lord God! Behold, I do not know how to speak, because I am a youth.” But the Lord said to me, “Do not say, ‘I am a youth,’ because everywhere I send you, you shall go, and all that I command you, you shall speak. -Jeremiah 1: 4-7

Despite Jeremiah’s fears he listened to God’s voice and obeyed His commandments. Jeremiah ended up writing the longest prophetic book of the Bible, covering a span of around 40 years. He was most likely a teen when he became a prophet.