Local authorities around the country are being urged to start planning now for an end to global population growth, expected to hit by the end of the century.
Nicky McDonald from the Nelson City Council said New Zealand was still young compared to other countries, which were already preparing for a looming end to population growth.
A United Nations report said a reduction in birth rates globally would lead to slower population growth and older communities, which was projected to have a profound effect on societies.
Ms McDonald said 200 years ago there was no country in the world with an average population age over 40. These days there was not a single country under that.
New Zealand was well behind the global conversation, which is the basis of a seminar - The Long Game - in Nelson this week.
"Communities are never going to return to what they were, because people are living longer, there are less children being born, and what it's going to mean is really an end to growth ... by the end of the century the world will stop growing."
It would top out at between nine to 11 billion people, she said.
The UN Department of Economics and Social Affairs report, published in June this year, showed that more countries had birth rates below what was required for the replacement of successive generations.
Ms McDonald said the UK was well advanced in its planning, while Japan led the way based on projections it would lose a third of its population by the end of the century.
"It was a bit of a wake-up call for me seeing countries that were much further advanced, but the solutions are beyond what any council can deliver because it's going to be such a massive change.
"We [councils] can provide the scaffolding but really, communities are going to have to get to grips with this," Ms McDonald said.
RNZ asked Auckland Mayor Phil Goff about how New Zealand's largest city was positioned to manage an ageing population. A spokesperson said it was not something the city was likely to experience in the short or medium term.
Local Government New Zealand president Dave Cull said the smaller regions of New Zealand were ageing faster than urban centres, and that would have an impact with fewer people able to afford higher rates.
More people would find themselves having to work longer.
"I think one of the key questions is, 'how can we support our changing population in ways that enable older people to keep contributing to communities?' and make decisions around sharing the burden of that," Mr Cull said.
Another challenge would be the varying rates of change in areas throughout New Zealand, especially those that attracted high numbers of tourists.
'There's a lot of thinking to be done now'
A consultant, who helps organisations in Australia and New Zealand to be more age-friendly, said employers were unsure how to work with that.
Geoff Pearman said the over 50s age group was now one of the fastest growing segments of business start-ups.
"I lost my job twice in my late 50s and decided I wasn't going to go through the whole process of trying to apply to get a job with another employer.
"Unconscious bias, discrimination - whatever you want to call it, is very real, so I positioned myself to move into establishing my own business."
Mr Pearman said older workers made a legitimate contribution to the entrepreneurial sector in New Zealand.
Ms McDonald warned failure to plan now meant society would not be ready when change started to bite.
"We think in the next couple of decades at least a third of all territorial authorities will have stalled in terms of growth, or moved backwards. So councils with fewer people, and more in difficult circumstances financially - there's a lot of thinking to be done now."