If the answer above is None it means there is no specific mention in the legislation, but you still need to ask local law enforcement before drinking in Liberia.
It is prohibited to sell, serve or supply alcohol beverages to anyone under the age of 18 years; this section shall not apply to a parent or guardian who serves an alcoholic beverage to his child or ward Penal Law of 1976 Sec 16.
You can find more legal details and links here:
Wikipedia Legal Drinking Page