No minor under the age of 16 years shall be employed or permitted to work as a messenger for any telegraph, telephone, or messenger company, or for the United States government or any of its departments while operating a telegraph, telephone, or messenger service, in the distribution, transmission, or delivery of goods or messages in cities of more than 15,000 inhabitants; nor shall any minor under the age of 18 years be employed, permitted, or suffered to engage in such work before 6 o'clock in the morning or after 9 o'clock in the evening. Nothing in this section shall apply to any minor employed to deliver newspapers to consumers.