they are rookies because they have not been pirates for very long. thats what makes them rookies and that why they got titles of "super novas" because its rare/impressive for rookies to get to 100 mill. and also the got that title because it rare for so many 100 mill rookies to pop up at the same time. but as said, age has nothing to do with being a rookie. like in sports it matters when you start not how old you are.