Zim planned on getting more 'educated' in human anatomy.. Now he could have taken practically any filthy human on earth over the age of 17, yes; But who does he kidnap to his base? Dib.
Zim
"GREETINGS filthy worm babies! You earth monkey's should appreciate being able to make any contact at all with YOUR GREAT AND POWERFUL INVADER! Even if it's through a screen.."