Originally Posted by
garykung
Yes, except that when the aircraft is within a country's airspace.
The problem is there are many islands/atolls in the Pacific Ocean that are controlled by the U.S. In addition, despite being international airspace, many airspaces within the Pacific Ocean are under the U.S. control. IMHO - I would say NZ will impose the 21 limit almost the entire way to AKL once departed.
However, you are welcome to try your lucky. Simply don't expect anything.
Incorrect the drinking age on NZ is 18 no matter were at the aircraft is departing from, what matters is the country of registration of the aircraft.
New Zealand controls most of the airspace in the South Pacific, and also have an few pacific island territories that cover large amounts of the pacific ocean.