Saul the king

^19-20 “I’m the Seer,” said Samuel. “Accompany me to the shrine and eat with me. In the morning I’ll tell you all about what’s on your mind, and send you on your way. And by the way, your lost donkeys—the ones you’ve been hunting for the last three days—have been found, so don’t worry about them. At this moment, Israel’s future is in your hands.”
²¹ Saul answered, “But I’m only a Benjaminite, from the smallest of Israel’s tribes, and from the most insignificant clan in the tribe at that. Why are you talking to me like this?”

This verse is impactful. 
But i am only a Benjaminite...
  
Do this not sound familar?
I am only a student... I am only a ...

We also do this, we limit what we can do or not do by our own strength. It may be true that you are just a 18 year old... just a student.

However, you have God's strength and power residing in you through Jesus Christ and the Holy Spirit. Though you are only a child, God can use you to glorify His kingdom. Similarly, God used Saul who is just a farmer to rule over Israel and to be a king. 

Even Saul himself did not have that faith in himself. He answered But i am only a Benjaminite, from the smallest of Israel's tribes, and from the most insignificant clan in the tribe at that. 

This really tells us, if God can use Saul to be king. He can use us too! Have faith!