It’s important to consider that a 9-year-old still is very young and has a lot of time left to develop creative writing skills. When I was 9-years old, I too had no interest whatsoever in creative writing, and I did not even read books. You have to encourage him step by step, gradually, to read first and then learn the creative writing skills. Adventure and mystery stories are generally preferred by that age group. You can try reading aloud if he doesn’t want to ready by himself. Also, don’t forget to be patient – a mindset doesn’t change quickly.
I had my ELLs create an invitation using your lesson. After choosing the event, we brainstormed together, using a concept map, what would need to be included. Then I made like a story map for them to fill in with the required info. For my lower ELLs, I used frames: Please come to my ____ on ____ at ____. They referenced the vocabulary we brainstormed and that I had written on a chart. After drafting, we did peer edits, from a specific check list, and revised and edited for specific errors based on peer edit. It went really well and studets enjoyed decorating their invitations as well!