That's now how it works. Lots of people express developmental stuttering in their teens. I know some who only started stuttering at 18, 19 years old. You didn't do anything to create this and thus, there's nothing you need to "fix". If you can stop trying to fix this part of yourself and learn to take it in stride and not care so much about it, life will be better and you'll be happier (and the stutter's impact on your life will diminish as well).