But he is coming under increasing pressure to discuss future impacts.
In the hard-hitting advice on superannuation, the Treasury says leaving the retirement income settings in place would have to lead to higher taxes, which would harm growth, or large cuts in spending on other areas such as health and education.
It says that as the baby-boomers move into retirement, New Zealand's 65-and-over population is projected to grow nearly four times more quickly than the total population over the next 15 years, contributing to a rapid rise in health, aged care and New Zealand Superannuation costs.
"The resulting fiscal challenge is considerable and there is no way to avoid making tradeoffs," the Treasury says. "Given the potential economic and social instability that could result from any uncertainty about these tradeoffs, we think it is crucial that effort be made to build broad public consensus on the way forward."
It says the current acceleration in the growth of the older population makes it "a matter of priority for New Zealand".
The briefing paper says that on past experience, when the age of super was lifted from 60 to 65 in the decade to 2001 it helped to reduce costs because people stayed in the workforce for longer.
Comparing New Zealand's age with other countries in 2010, 2030 and 2050, it shows that Australia's age was set at 65, 66, 67; Britain 65, 66, and 67; and the United States 66, 67 and 67 - though the age for women in 2010 in Britain and Australia was 60 and 62 respectively.
HOW NZ COMPARES
Britain*
Currently 65 for men, rising to 66 in 2030 and 67 in 2050
Australia*
Currently 65, rising to 66 in 2030 and 67 in 2050
United States
Currently 66, rising to 67 in 2030
New Zealand
No planned change
* Women can currently retire at 60 in Britain, 62 in Australia