When writing a 'Percy Jackson age play fanfic', it's important to really understand the source material. Know Percy's backstory, his strengths, and his weaknesses. Then, when you introduce the age play, think about how it changes everything. For example, his training at Camp Half - Blood might need to be redone. His relationships with the gods and other demigods will also be different. You can start by creating an outline of the story, with the main plot points centered around Percy's age - changed situation. Include details about how he looks, behaves, and thinks as a younger version. And as you write, let your creativity flow. You can introduce new characters or sub - plots that are related to the age play concept, like a young Percy befriending a new demigod who helps him understand his new state better.
To write a 'Percy Jackson age play fanfic', start with a strong concept. You could base it on a specific event in the original books and then twist it with the age play element. For instance, if Percy was turned young during the Battle of Manhattan. You should also pay attention to the relationships. How will his friends like Annabeth and Grover react? Will they be more protective? Develop the story gradually, showing Percy's growth or struggle in his new, younger state. And don't forget to add your own unique touches to the story, like new magical elements or character backstories related to the age play.