The federal minimum wage is 5.15 /hr, regardless of age.
States are allowed to have their own labor laws, however, and can therefore have their own individual minimum wages. Federal law entitles citizens to whichever wage is higher, so states can really only have higher minimum wages than whatever the federal currently is.
In California, I know that the minimum wage is somewhere around $7.00 /hr. Tennesse is 5.15
