(a) It shall be unlawful for any person under the age of 21 years to remain on any premises where the sale of alcoholic liquor is licensed for on-premises consumption, or where a caterer or temporary permit holder is serving alcoholic liquor.
(b) It shall be unlawful for the operator, person in charge or licensee of any premises licensed for on-premises consumption of alcoholic liquor or a caterer or temporary permit holder who is serving alcoholic liquor to permit any person under the age of 21 years to remain on the premises.
(c) This section shall not apply if the person under the age of 21 years is accompanied by his or her parent or guardian, or if the licensed or permitted premises derive not more than 30% of its gross receipts in each calendar year from the sale of alcoholic liquor for on-premises consumption.