The idea that New Zealand's ageing population will be a huge drain on the economy is mostly false, say the authors of the country's biggest ageing study.

The latest report from Massey University's long-running study of 11,000 older New Zealanders shows two-thirds of them are in good physical and mental health, and that many want to keep working.

"They're not all the same aged person whose health is declining and who will become a health problem in future," said Massey University researcher Christine Stephens.

In all, 62 per cent of the study's participants - now aged between 65 and 81 - had remained in "good" or "robust" health since the study began in 2006.

That meant they had no illnesses, were able to carry out daily activities without assistance, did occasional exercise, had no signs of mental health issues like depression, and were socially active.

Yet in 2016, there were more over-65s registered as seeking jobs than 18 to 24-year-olds – a reversal of the data from five years earlier. Ageism was partly to blame.

The latest report from the Massey study, published today, comes as New Zealand's over-65 population is predicted to double within 30 years.

"There is this perception that there is going to be this great drain on the economy because of the ageing population," Stephens said.

"The other side of that is not only is there a good proportion of people who are doing just fine and whose health is not declining, but can and want to remain in the workforce."

Compared to other developed countries, New Zealand has a relatively high employment rate for people aged over 55. But the unemployment rate for older people is rising, despite efforts from Government, businesses and unions to encourage hiring of people over 55.

Grey Power Auckland president Anne-Marie Coury said she knew of older people who had structured their CVs to make their age less prominent or disguised their voice in phone interviews.

"Some people with high energy can sound young on the telephone, but when they go into the interview, the looks on the people's faces tell them they are 10 years older than the employee they wanted," she said.

"They realise they are just going to go through the motions. That's really quite soul-destroying to go through a number of those interviews in a row."

Coury said some employers had made a point of hiring older workers, like supermarket chain Countdown and hardware company Bunnings.

But retail or physical work was not for everyone: "Do you want to stand on a concrete floor 40 hours a week? I certainly wouldn't want to. I want to use the brain skills I've developed."

While the report was broadly positive about older people's wellbeing, there were also some concerns about housing security and affordability for older New Zealanders.

At a time when home ownership rates are falling, the study found that older people in rental housing had poorer mental health.

"These groups need the most policy attention and also highlight that not all old people are rich baby boomers," Stephens said.