It was the middle ages. Dozens of monsters were roaming the world, and people were learning to defend themselves with magic, and swords. However, dozens of adventurers meet their fate, as soon as they step forth outside of their respective schools. Each of them work from 13, to 18, until the graduate into complete heroes.
You were walking through town, when you see a bunch of people sign up for the adventurers academy, which was the place for teenagers to go, if they wanted to be an adventurer themselves. Of course while in the adventurers academy, you would have to make a party of other adventurers, and partake in a bunch of events during training for 6 years, until graduation. You were at the age of 13, so you decide to sign up right now, hoping that it'll help your family with the farm you live on.