No person shall give or furnish any alcoholic beverage to any person under 21 years of age, except upon authority of and pursuant to a prescription of a duly licensed physician. Further, persons in charge of any establishment where alcoholic beverages are sold or furnished for consumption, either on or away from the premises, shall have the right at any time to demand of any person offering to buy or drinking any alcoholic beverage proof that the person has attained the age of 21 years.