All minors must have a parental consent. Therefore, you would have to have your design submitted by a parent or legal guardian. The parent or legal guardian has to verify that they have read the rules and agree to them. The parent must also agree to the parental consent form.
Submissions cannot be deleted. However, they can be altered. If someone has posted a submission, but would like to put a photo or other placeholder in where the design is, Challenge.post has said that submitters have the ability to do this.