Add an amendment to the constitutions reading as follows: "The right to vote shall not be denied any citizen of the United States for any reason whatsoever."
Minors and felons are ruled by a government in which they cannot participate. This violates the principle that no government is legitimate that does not ask the consent of the governed. It is not legitimate for any citizen to deny another's right to vote on the basis that they do not trust the choices they might make.