Youngbeliever,
If I may share my story to hopefully encourage you.
I received the call to preach my freshmen year in college. This was 180 degrees from being an officer in the USMC but, non the less, I gave up on that and set my sights on the call. Since then I've been through many twists and turns in my life and have ended up in the place where I believe God wants me. I preached two messages in college that seem to have been nothing more than confirmation of the call. It was 3 years before I got to preach to a congregation again, that was this summer. In the meantime I was filled with an unquechable desire to preach and seemingly no outlet. Soon I became content with it and realized that God would use me when He needed to. People would ask when I was going to preach and I just told them that I was in the oven cooking and when I was ready God would take me out and use me. I needed, and still need, time to mature and grow and learn more about God, I assure you God will use you when the time comes. Explore this calling and soon, if it's for real, there will be no escape from it.
You also mentioned being scared and feeling unprepared. Well, I don't think one ever gets over being nervous about preaching. It's a great responsibility but being a part of the body of Christ is a great reward. Plus, if you are called to preach then there is absolutely nothing more perfect for you to do, no better way for you to fulfill God's will for your life.
Practical things:
1. Take public speaking courses. These were invaluable to me in learning how to address people en masse.
2. Remember, you're not a showman, you're there to be the megaphone for God.
3. Study without ceasing, pray without ceasing and seek the very face of God.
4.Before all else remember that it's not you that matters. It's not what
you have to say but the message of
Christ through you.
5. Don't let anyone look down on you because you are young or because of your particular circumstances. If it mattered where we came from then Paul would never have been an apostle.
6. Don't be afraid, we've been given a spirit of power not a spirit of timidity. Nervous is okay, but not afraid. Christ Himself said, "be not afraid, it is I."
7. Be patient and accept God's will.
I hope this was of some help and encouragement, if not then just ignore it.
Godbless and Godspeed.