If you continuously see yourself prophesying in a dream, this is a sign God has called you into the prophetic ministry to be His servant. God can call you at any stage or age in life. He called Jeremiah when he was approximately 17 years old.
God also called Moses when he was of age, 80 years old, to be a prophet and leader of His people. In the dream, you may see yourself prophesying to the nations, and leaders, or even performing miracles by The Spirit of God. This is a clear confirmation God is calling you into the ministry which He predestined for you beforehand.
Related: What are conditional prophecies?
I remember seeing myself prophesying to various nations and ethnic groups as well, performing miracles by The Spirit of God. I knew very well that God had called me to be a minister of the good news. I used to have frequent dreams about things to come and matters concerning people I knew and others I had never met.
How to protect this dream
You should protect your dreams, lest the enemy snatches them from you to be used for witchcraft. Therefore, you must dedicate your dreams to God for protection and fulfillment.
This is a good dream and therefore, you should ask God for wisdom and patience as He prepares you for the task ahead. Consider doing a personal dedication for your consecration and devotion to God.