User blog comment:KidVegeta/KidVegeta's reviews/@comment-1954732-20101102163117/@comment-3097771-20101102190051

17 and 18 were confirmed much later. They were taken as children, and weren't all that much older in their introduction saga. I think you're confused on what it means to "start". Gero doesn't need all the DNA to start Cell, he needed it to finish him. Obviously, early on he had DNA of Goku and Piccolo... and even thinking up a concept, drawing designs (which is implied that he did before gathering DNA) counts as starting work on Cell.You don't just start gathering DNA of the world's greatest warriors for no reason, with no plan. -KidVegeta