If any person is, by reason of minority, mental illness, or other disability, incapable of making any declaration or doing any act required or permitted by this Act, then the guardian, curator or other legal representative (if any) of such person or, if there be none, any person appointed by the court upon application on behalf of the person under disability or on behalf of any other person interested in the making of such declaration or doing such act, may make the declaration or a declaration as nearly corresponding thereto as circumstances permit, and do the act in the name and on behalf of the person under disability, and all acts done by such substitute shall, for the purposes of this Act, be as effectual as if done by the person for whom he is substituted.