Find the first and last name of students whose age is younger than the average age.
return students ;return ages of  #1 ;return the average of  #2 ;return #1 where  #2 is  less than  #3 ;return first name of  #4 ;return last name of  #4 ;return #5 ,   #6
['select', 'project', 'aggregate', 'comparative', 'project', 'project', 'union']