There are two endings for the game -

1. Play the game as normal.

2. If you save the blue dragon during the teenage years by not killing them, you will get a key item from him.

During the time when you return to the castle and are preparing to leave, head back to the area where you got said key item from, you'll find a dragon statue in the area. Interact with it and then choose to gain power from a certain NPC, use said power consecutively and you will get a different ending during the end of the teenage years and the game itself.