Hey!
Yesterday, I downloaded a model I’d been working on from Google Drive. I opened it and modeled for about an hour (in SU Make 17).
Today, I go to open the same file and it says “The file was created in a newer version of SketchUp”
Hello, it means that at some point it has been opened and saved from SketchUp 2018.
You can drag and drop it in SketchUp for web (free), it will be imported as a component, and download it again as 2017 version