Eclipse Not Working?

I am trying to get back into modding after not doing it for several years, and I am trying to get Eclipse, Forge, JDK etc. all set up on my new PC. I followed a few different tutorials to get them installed, but I keep getting this error when I try to run the gradlew commands in cmdprompt or when I launch Eclipse:

"BUG! exception in phase "semantic analysis' in source unit '_BuildScript_' Unsupported class file major version 67

Does anybody know how to fix this, or where I went wrong?



Thanks!