Do you know the difference? If an actor is Legal 18, it means they are done with high school and can work without a studio teacher, either they have taken and passed the CHSPE or they have graduated early. They no longer need a parent on set but must have a parent sign contracts. They can also work longer hours. Emancipated means that their parents are no longer their legal guardians so they can sign their own contracts, but they still need a studio teacher and cannot work longer hours.
For more on this, read this Bizparentz article on Emancipation.