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 Tunisia.
Law 2004-75 Article 4 prohibits entry to night clubs to those under 18 with an exception for accompanied persons between 16 and 18 in certain venues, sale of alcohol beverages to whom is prohibited.
You can find more legal details and links here:
Wikipedia Legal Drinking Page