Hey...great question. So, I have written about this in some of my blog posts and it seems you don't need a high school diploma or GED. I actually went one step further and called two locations in different states to confirm this and they said the following -

You need to be 17+ years old with a California ID or Drivers License. Here are the two CNA training schools I called. You can see the information for yourself -

https://www.aplusnursingschool.com/courses.html

https://www.h2hhealth.com/certified-nurse-assistant-cna-2/

Also, I personally recommend having a high school diploma and/or GED because it just prepares you to be in the study mode. If you've been in school before, you won't have any trouble getting into study mode. However, everyone is different and some people without any schooling have no troubling studying when they have too 🙂