Java script for specific age calculation

I need to create a simple age calculator to determine if a user is allowed to purchase a particular restricted product. I need to model an abstract class to represent the generic restricted product and concrete classes to represent alcohol, tobacco, R-rated movies, PG-13 rated movies and video games. Each of these products have a different minimum age for purchase. The age calculator user interface will be a Java Swing application that instantiates the product selected by the user and compares its minimum purchase age with the birthdate of the customer. If the customer is old enough to purchase the product a dialog box to that effect appears. A rejection message is displayed if the customer is too young.