It is unlawful for any person maintaining or operating any of the games or slot machines to allow any person under the age of twenty one (21) years to play any licensed game or slot machine or loiter about the room or premises wherein any game or slot machine herein mentioned is operated or conducted, and in any legal action it shall be no excuse by the licensee, employee or dealer operating or conducting any licensed game or slot machine to plead that he or they believed the party or parties to be twenty one (21) years or older. (CH Ord. 6 § 10, 1946)