dude, go and play some juniors first
you got no chance of playing Challengers (not even Futures) if you are not good enough in ITF Under 18 tournaments
This is completely not true. A lot of players do not play the junior circuit at all, or only barely, before they start to take part in Futures, Challengers and ATP level events. For many, juniors is a logical step, but it is by no means a necessary step as you make it sound.
My advice would be to not get your hopes up. You are much more likely to be unsuccessful in getting these WCs (let alone winning matches) than in obtaining them. However, if you are set on getting WCs, you will need to convince people of your talent. I would aim for Futures WCs, as they are more easily obtainable (esp. Futures qualies). Right now, at the age of 14, you stand no chance in Challengers whatsoever anyway. However, if you feel over-confident, some Challengers do sell WCs to the likes of Kevin McDuffee and Erwin Kerkhoven, so I don't see why you couldn't get one if you offer enough bucks.