I've been looking through search engines and cannot find that there is a law. But does not mean there is not. And I would agree that you can not base by childs age but by maturaity. And I would not leave my children home alone no matter how mature until middle school to consider it.
There isn't any law that states a specific age, but chapter 827 of the Florida Statutes does spell out what child neglect is, it includes not providing adequate
supervision for a "child". The definitions state that a "child" is anyone under the age of 18, so it's decided on a case by case/situation basis. Basically, in Florida, even if the child is 17 and is left alone, the parent/guardian could face neglect charges if the child is injured while left alone.