The Treasury has suggested New Zealand raise the age at which people qualify for government superannuation.
In its briefing for incoming ministers, it says government finances will come under growing pressure as baby-boomers retire.
At the general election in November last year, the Labour Party called for a gradual increase in the age of eligibility for superannuation from 65 to 67.
Prime Minister John Key raising the age is not necessary.
But the Treasury says the over-65 demographic is projected to grow four times faster than the rest of the population over the next 15 years - making superannuation, health and aged care more expensive.
It notes that Australia, Britain and the United States have already started raising the age of the eligibility for the pension.