This means Armageddon cannot come when everyone is prepared. You are always going to have a certain number of children just below the age of accountability--and, by the time you reach every single one of them, another batch will be right at that age. This process never ends as long as children are born.
As for their promise that "the end is close, and getting closer", that doesn't add up either. If you disobeyed the hounders and paid attention to ninth grade algebra instead of your Washtowel, you would understand what happens when you graph equations. You can get equations that forever approach a certain line--but never quite get there. When graphed, they are close to these lines, and getting closer--but never will they actually reach those lines. True, they might appear to, usually because of finite resolutions and/or sloppy plotting of your graphs (which is unavoidable). But, if you had infinite resolution and zero sloppiness in plotting, you would see that the graph of the equation never quite crosses those lines. The simplest example is Y=1/X; Y=0. You have simultaneous equations that are forever getting closer, but there is no root (or point where they cross).
The reason the Washtowel doesn't want you paying attention to algebra is simple. If one equation can be forever getting closer to another without their being a root, then why can't another? What if Armageddon is one equation and real time is another--forever getting closer, but never intersecting? Supposing Jehovah is simply plotting real time as Y=1/X and Armageddon as Y=0? Since X is very large by now, Y is very close to 0 but will never reach 0. Similarly, it is possible for Armageddon to never happen--and if it doesn't, the witlesses will be wasting all their time and bearing a huge opportunity cost simply for nothing. And, if any gained back their wits, they would simply quit.