If you're using the
java command directly, it'll use the version set in your
PATH environment variable (if you're using Windows). If that's pointing to an older version of Java, it'll try to use that one. When needing to manage multiple different versions, it's generally easier to specify the full path to the correct Java installation to use. so instead of using something like
java -jar paper.jar, you'd use
\path\to\correct\java\installation\java.exe -jar paper.jar. This will ensure it uses the java in that directory, rather than whichever one
java is pointing to.