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 Brazil.
It is prohibited to sell, serve or supply any alcohol beverage to a person under 18 years of age. The presidential law enacted on March 17, 2015 made any violation of the law a criminal offence. Any adult person selling, serving, giving or supplying alcohol beverages to a minor is punished with imprisonment of 2 to 4 years, a fine of R$3.000 to R$10.000 and a ban to operate any business selling or serving alcohol.
You can find more legal details and links here:
Wikipedia Legal Drinking Page