Heather du Plessis-Allan: Happy 25th New Zealand First - now grow up

COMMENT: In this country you only reach full adulthood at 25.

At 17 you can join the army. At 18 you can drink. At 20 you can gamble in a casino. At 24 your parents' income won't count against government assistance for your studies. And at 25 you can adopt a child who isn't related to you.

After that, there are no more age hurdles telling you you're too young. After that, youthfulness is no excuse for bad behaviour.

Funny that, because New Zealand First turned 25 on Wednesday. Which means it's time for the party to grow up a little.

First, credit where credit is due. This is a party that has defied the odds repeatedly. Let me run you through the top three.

It's amazing New Zealand First even exists. It's incredibly difficult to get a political party off the ground in New Zealand. The Conservatives tried and couldn't. Gareth Morgan tried and couldn't. That's despite both of them having millions of dollars to spend.

Second, it's amazing that the party has made it to 25. Twice, we expected New Zealand First to die. The first body blow was when the party split in 1998. But, New Zealand First survived. Then the country booted the lot of them out in 2008 and we all thought, right-oh, that's the end of that then. That's what normally happens when a party gets the heave-ho. Think Hone Harawira's Mana. Think The Alliance.

But New Zealand First came back.

Three years later, there was Winston's blink-blink smile back in the camera lights.

Third, the party has consistently punched above its weight. It's been in three governments, held the Deputy PM job twice, the self-created Treasurer's job once, a total of 10 Cabinet positions, a bunch of positions outside the Cabinet.

It has screwed money for the Super Gold Card out of Michael Cullen's punch-tight fist, screwed $3 billion for regional splash cash out of Jacinda Ardern, screwed $1 billion for diplomats and foreign aid at out the same government and rounded it off with $2.4b for planes and missiles.

Now the party's founder is running the country for six weeks.

There's a lot to celebrate.

Problem is, as I said, there's a bit of growing up to do.

New Zealand First is juvenile in the way it shows off the cash it's managed to force out of Ardern. Announcing the plane spend in the same week the nurses went on strike for better pay was unfortunate timing.

That's if you think the timing wasn't deliberate.

But, if you think it was deliberate, then the announcement was designed to underline just how powerful the party is. Juvenile right?

Pork barrel politics is only appealing to those getting the cash, and even then, it feels slightly dirty. Right now, Shane Jones is deliberately jetting around the regions, spending up large and hoping we all notice. New Zealand First looks like the guy at the bar who just got his first pay cheque from a job everyone knows he's under-qualified for.

Then there are the immature attacks on corporates. Peters, Jones and some MP called Mark Patterson clearly think punters love it when they take on the big boys.

They've attacked Fonterra, Air New Zealand, The Warehouse and a meatless burger. Some punters may toot and holler in approval, but only in the same way that school kids enjoy the class clown giving the teacher lip. That kid might be popular, but he doesn't get to be head boy.

Of course, New Zealand First doesn't have to grow up if it doesn't want to. It could keep playing the rogue. That tactic delivers just enough votes to keep bringing the party back into Parliament. But if they want another go at being in this Coalition Government after the next election, if they want another go at being as powerful as they clearly are right now, they may have to convince the voters that they can use that power responsibly.

Doesn't look that way yet.