Md. Code, Alcoholic Beverages and Cannabis § 6–309

(a) A license holder, a proprietor, or an operator of an establishment that provides alcoholic beverages may not allow on–premises consumption or possession of alcoholic beverages by an individual under the age of 21 years, regardless of who purchased or obtained the alcoholic beverages.

(b) In addition to any other penalty under this article, a license holder, a proprietor, or an operator who violates this section is guilty of a misdemeanor and on conviction is subject to a fine not exceeding $50.