Labour ministers are considering whether to allow 16-year-olds to vote in council elections - an easier task than for central elections.
National says its entire caucus would vote against legislation to make the voting age 16, making it extremely unlikely to pass because such a change would require a supermajority in Parliament - three quarters of MPs.
However, making the change for local body elections would only require 50 percent of MPs - and Prime Minister Jacinda Ardern said they had not ruled out tackling that separately.
"Haven't ruled that out, but again we only received this significant decision from the Supreme Court yesterday," she said.
"Parliament now has six months to debate and then return a decision, in that time we'll take some advice on the differences, for instance, in how local versus central government elections are treated."
She also confirmed the bill would be a "free vote", meaning MPs could vote as they wanted on the legislation, at least in the Labour Party.
Ardern yesterday expressed personal support for a lowering of the voting age, but said her vote was just one of 120 MPs and it would be a matter for Parliament as a whole.
Deputy Prime Minister Grant Robertson said local government may offer a way to see how it worked.
"Obviously we can all see that in order to get that supermajority it's going to be pretty hard for central government - I think local government does offer an opportunity, potentially, to road test it but obviously there'll be more discussions about that."
Robertson said he was personally supportive of a move to lower the voting age, but it should be accompanied by more civics education in schools.
"I have said for some time now I accept a reduction in the age on the grounds that there is a group of people who we make very important decisions about.
"I would like that group of people to have more opportunities to learn more about the way government systems work, the way our society works, but I think we can make progress on both."
The ACT Party has also said it opposed lowering the voting age, but leader David Seymour this afternoon said they would be fine with a change at the local government level.
"Yeah I don't see a huge problem with that - as the Supreme Court has noted the restrictions on Parliamentary voting don't apply to local body elections ... and I think maybe a bit of training wheels on the local body mightn't be a bad way to go," he said.
"I guess you can't do quite as much damage electing a bad council as you can electing a bad government, so not a bad place to try."
He said ACT MPs could vote as they liked on the legislation.
"We'll let our MPs vote individually - but as far as I can tell there's not a lot of appetite for voting at 16 within the ACT caucus."
"If you look at all the challenges New Zealand faces right now this can hardly be a priority, second of all they haven't really made the case."
Labour MPs heading into a caucus meeting this morning were largely supportive of a lower voting age - with the exceptions of David Parker and Willie Jackson.
Jackson said he had supported eligibility at 18 for a long time, but could potentially be persuaded.
"I understand all the arguments and I'm listening to colleagues about it but I'm a bit different I suppose, having worked with a lot of young people, but I could be persuaded. We'll see," he said.
"Working with young people I've put a lot of young people programmes in place and all that - I think it would be good if they got involved in politics but I just wonder in terms of their priorities whether they're really there."
He was supportive of more civics education in schools however, saying if that was put in place he might reconsider lowering the voting age.
Parker said people put an emphasis on different factors.
"My personal view is I'm happy with 18, for me it's a combination of: still depend on their parents, can't serve in the military, and often at school at the age of 16."
Greg O'Connor was among the most supportive of a change.
"For two weeks I've had kids in from Newlands College and Tawa college - all under 16, none of them will be eligible to vote next year - but all of them will be a heck of a lot better informed on their voting than they will be when they leave school.
"I think there'll be more informed voting will take place between 16 and 18 than probably does afterwards, so I'm a big believer in it ... I'm more than a believer in it, I'd actually be an advocate of it."
Associate Education Minister Jan Tinetti was also in favour.
"I've worked with lots of kids over the years, I know that there's - with our young people - a growing fascination, a growing ability to understand complex issues.
"I know that they're excited about the issues, I know that this is their world that they're moving into - they have the ability to do this. These young people that we have today are amazing."
Voting age not a conscience issue - National
National leader Christopher Luxon made clear the party was united against changing the voting age.
"We'll have the debate and discussion but our position's pretty clear - we think 18's about right," he said.
"You've just to to rule the line somewhere, there's pros and cons for doign that, on balance we think that 18's the right age."
He said the caucus had a conversation about the matter several months ago and "we all came out very aligned ... I can tell you our party position's really clear, we just can't see any reason to move it from 18".
In practice, parties can largely decide whether to treat an issue as a conscience vote or whether the caucus will be "whipped" into supporting a particular position, which is then signed off by the Speaker - so while Labour MPs will be voting individually, it's up to the other parties whether they would do the same.
National MP Chris Bishop said it was not a conscience issue for the party.
"It's not a consience issue for National Party MPs. I see the prime minister say yesterday that the speaker will decide if it's a conscience issue or not - actually she's wrong, it's not the speaker's deiciosn, it's not her decision, it's the party's decision."
Bishop said he was not in favour of lowering the voting age.
"Eighteen is the age at which you attain adulthood in New Zealand. It's the age at which you can legally buy alcohol, it's the age at which you can enter into a contract of your own volition, it's the age at which you can get married without special permission from the court.
"I was a politically engaged young person but I'm very comfortable with the voting age being 18."
He said he thought the Supreme Court's finding was an example of overreach.
"Intruding into something that is fundamentally the realm of Parliament. These are political decisions for the Parliament to decide."
Te Pāti Māori co-leader Debbie Ngarewa-Packer said they supported lowering the voting age, and National should too.
"It's good, I would hope that ones like National would support it because if 10-year-olds are old enough to be able to go to military boot camp then they must support 16-year-olds being able to vote."
David Parker - who is the Attorney-General - said while he had been surprised by the Supreme Court's decision, it was the right of the court to make those decisions.
"I'm not criticising them, they've approached these decisions independently," he said.
He also clarified the court's decision - which was in response to a case brought to the High Court and Court of Appeal - was not a finding of a breach of the Bill of Rights Act but rather that the current age had not been justified - yet.
"What they found was that the case proving that it was justified was not proven - they didn't say that it couldn't be justified, they just said it wasn't."
That would in part have been because the Crown declined to defend it.
"The Crown didn't think it had an obligation to prove the policy position, and the logic that was relied upon by Justice Kós in his minority judgement was clear on the court record from the court of appeal submissions on that very point," Parker said.