"Then I said, 'Ah Lord God! Behold I do not know how to speak, for I am only a youth.' But the Lord said to me, 'Do not say "I am only a youth" for to all to whom I send you, you shall go, and whatever I command you, you shall speak. Do not be afraid of them, for I am with you to deliver you,' declares the Lord." --Jeremiah 1:6-8
In this passage God commands Jeremiah to speak to the people on His behalf and what does Jeremiah do? "I do not know how to speak, for I am only a youth." This wasn't an easy task, nor would it be a fun task, or a task where the people would love him, it was a difficult, uncomfortable hard task. Jeremiah thought himself too young. Jeremiah didn't think that God could use him because of his age. But what does God say? That HE would be with Jeremiah, give him the words to say, and deliver him. God doesn't just command him to do something, he also gives us promises to go with that command.