"But we had reached a certain point with our characters - when they started they were 25, but by the time we finished the last series, they were about 30. The series was always meant to be about that quarter-life crisis, trying to figure out what to do with their lives, but that was no longer really applying to the characters. We were sort of at a stage where they were settling down, having babies - they were really about to join the team at Nothing Trivial."
Which is fair enough, although the practical problem that really pushed the change, was that previous cast members have moved on.
"Yes, we also had some availability issues with some of the actors," Lang explains, "because they've become famous and they're moving offshore. We worked around it on season four, but it was tricky, and it's an ensemble show, you need the whole team."
Jay Ryan (Kevin) is now appearing in US TV series Beauty and the Beast, Anna Hutchinson (Amy) is in the final series of Spartacus and has moved to the US for further work, while Esther Stephens (Olivia) has moved to Australia to pursue her music career, and Matt Whelan (Brad) has been working on several local projects, including Three Mile Limit - a film loosely based on the story of Radio Hauraki, due out this year. Some might ask why they didn't simply finish the show then, but it wasn't a decision to be made lightly, especially given the show's popularity.
"We did look at all the different options of how to do it and we could've finished it at the end of season four, but we still liked the idea of the show. We thought, well, what would happen if we had a new bunch of 25-year-olds? And that was quite exciting.
"Things have changed quite a bit in New Zealand in the past five years, particularly with the recession, and I think today's 25-year-olds are dealing with quite a different world. It's quite interesting - our bunch of new actors, they're fantastic, but they're a very serious bunch. They've lived through harder times somehow."
So what can be expected from this new lot then? Well, Ted is the laddish, good-hearted landscaper, whose blokey exterior hides a more sensitive side, and he's taken over from Kevin as the narrator - Lang knew they needed to keep that aspect.
"The male narrator was always part of the show, it was the thing that made it different. Part of the Go Girls idea came from thinking about what Sex and the City would be like if you set it on the North Shore, but it was interesting to have a guy in the middle, and hear his take on their lives."
The relationships between the remaining characters have changed a bit though - Bennie is Ted's younger sister, and their flatmate Levi has been like a brother to them since his mum took them in after their parents split up and left, plus he's gay.
"In a way I think that's quietly radical. Levi is a great character, and having a friendship between a gay guy and a straight guy on TV is not something you see too often. Often the gay characters are the best friend of a girl, and are rather camp, like some sort of comic relief, but we're treating Levi's stories the same as anyone else's - he gets some great dramatic moments, and he gets a lovely romance, which is cool."
Then there's nerdy good girl Alice, who seems to have her life all mapped out - a job in insurance, marriage to her university sweetheart; and Candy, Britta's younger sister, the link to the old cast, whom everyone loves to hate.
"I think when we put Candy on the beach at the end of the last season, a few people went 'ooh', cos she's horrible, she's not well-liked, a terrible girl, but I adore her because she's so much fun."
They're not miles away from hard-working, hard-case Cody, or earnest, well-meaning Brad, or even whimsical Britta, and there's still very much a North Shore vibe to the show (a flat with views to Rangitoto, beach visits, modern houses, and more than one real estate agent), but it will be a bit of a shock for fans of all ages (you didn't have to be 25 to enjoy the show) who'd grown to love the previous go girls and boys.
"We're nervous obviously, because we've done something a bit radical," Lang readily admits. "We appreciate people's loyalty to the old bunch, but we just hope people will check it out and give the new characters a chance too."
What: Go Girls, season five
Where and when: Tuesday, April 30, 8.30pm, TV2
- TimeOut