Any licensee under an on-sale license issued for public premises, as defined in Section 23039, who permits a person under the age of 21 years to enter and remain in the licensed premises without lawful business therein is guilty of a misdemeanor. Any person under the age of 21 years who enters and remains in the licensed public premises without lawful business therein is guilty of a misdemeanor and shall be punished by a fine of not less than two hundred dollars ($200), no part of which shall be suspended.