Do 18 year olds need to have an instructional permit for 6 months before they can get a drivers license?

I know that all minors need to hold their drivers permit for 6 months before testing for a drivers license. Is it the same for 18 year olds?
Update: I live in California, so does anyone what the rules are here? I'm aware now that you need a permit before a license even if you're 18 years old, but is there a minimum amount of time that you must have the permit when you are 18 before you are able to get your license?
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