Peters warned provincial voters against backing National or the Act party.
"Do the mathematics. If they haven't got a hope of being the next government, then where's your insurance going for the next three years?"
New Zealand First was already in the government and had rural voters' backs, "when others would not have had," Peters said.
"We didn't sign up for the Paris Accord – the National Party did – and we've made sure that, for farming, it's not the devastatingly damaging potential policy that others would have [made] it."
"I think your listeners need to understand this; if you're going to vote for parties that have no effect at all on the politics of the next three years; then you're on the outside with your nose hard pressed against the window.
"And you can not afford to be there – you need someone to cover your back."
Mackay asked Peters if, at 75 years old, he was "suffering by comparison" against a young Prime Minister like Jacinda Ardern.
"Only when I get a comment like you just made there" Peters said.
He said Mackay's comment ruled out "700,000 people, many of whom make this country what it is."
"There are people doing all sorts of voluntary work, they're over 65, they've not stopped working – they're huge in the community – and they've dramatically been a force for good in this society."
"You've just – like other politicians – ruled them all out as being of any value in our society. That's disappointing."
Mackay said Peters hadn't answered the question, which was whether he was too old for government.
"The question is loaded with an inference and I'm just responding to it. I'm sorry - questions, words, matter" Peters said.
Listen below:
In fact, Peters said he had been getting "serious cut-through now" with social media, which Mackay said was a popular way of reaching younger voters.
Peter said his recent video on Twitter, where he drove a tractor to prove to Mackay that it was easy "had passed a million views".
Ultimately, the Deputy Prime Minister said he wasn't concerned by recent polls that put New Zealand First at 2 per cent.
"I don't think these pollsters know what they're doing and I'm not concerned – and if we're not going to be seeing you after the election it's probably because you're [Mackay] going to be retired from your job" he said.
Finally, Peters confessed to something else he wasn't that concerned about – last night's Leaders Debate between Prime Minister Jacinda Ardern and Opposition Leader Judith Collins – which he said he didn't watch.
"I didn't think it would be of any great interest frankly, and I'm told it wasn't."
Also in today's interview: Mackay and Peters remembered David Halligan, who died unexpectedly recently.
