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 Cuba.
The penal code prohibits any adult to induce any young person under the age of 16 years, to habitually consume alcohol beverages. However this means that de facto anyone selling, serving or supplying alcohol should check if the buyer has attained the age of 16 years. In most cases this law is not strictly enforced.
You can find more legal details and links here:
Wikipedia Legal Drinking Page