(a) It shall be unlawful for the owner, operator, manager, person in charge, or any employee of a sexually oriented business, as defined in section 26-441, to knowingly allow or permit any person under the age of 18 years to enter or be present in the premises of such business.

(b) It shall be an affirmative defense to a violation of this section that the person under the age of 18 years exhibited a fraudulent proof of age in order to gain entrance to the business premises. (Code 1979, § 23-20)