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 Vanuatu.
It is unlawful to sell, serve or supply alcohol to any person under the age of 18 years. Violation of the law is fined up to VT 25,000 or by a term of imprisonment not exceeding 3 months, or by both, fine and imprisonment. Any minor under the age of 18 years, being found in possession or consumption of alcohol is fined up to VT 10,000.
You can find more legal details and links here:
Wikipedia Legal Drinking Page