More than 500,000 New Zealanders will be able to join KiwiSaver due to law changes from Monday.
About 2.9 million people already belong to the retirement savings scheme, but until now, over-65-year-olds had been locked out of joining.
It is one of a handful of law changes which take effect on July 1.
There are 747,900 people aged 65 and over in New Zealand, according to Statistics New Zealand and research by the Commission for Financial Capability shows nearly one in three (29 per cent) of over-65-year-olds are already in KiwiSaver.
• Canny View: Key changes to KiwiSaver start kicking in from April
• More than $4 billion of KiwiSaver money invested in weapons, sin stocks and unethical companies: find out what your fund owns
• Battle heats up to become the cheapest KiwiSaver provider
• Explainer: How to change your KiwiSaver tax rate
That leaves 531,009 who will be able to join.
Martin Hawes, who sits on the investment committee of Summer KiwiSaver scheme, believed there would be strong take-up from the over-65s.
"The reason is because of falling interest rates, which in my view will be lower for longer."
Ten years ago, retirees could get 8 per cent interest just by putting their money in the bank, but term deposit rates have fallen to around 3 per cent or less.
"Anybody sitting in bank term deposits and who thinks it will go back to 8 or 9 per cent is doomed to disappointment," he said.
Editorial: Diligence needed over KiwiSaver 'sin stocks'
NZ govt's books in better shape than forecast on higher tax take
"These rates are the new normal."
Hawes said moving money into KiwiSaver not only allowed people to access a potentially higher return but also spread their money around different types of investments.
"With KiwiSaver, you have got a ready made diversified fund that is well regulated and cheaper than other managed funds."
He said a lot of retirees had $100k or $200k in savings which was too small an amount to get access to professional financial advice and KiwiSaver was a convenient way of getting that.
The Government's Smart Investor website shows the average fee for a conservative KiwiSaver fund is 1.1 per cent, or about $110 a year, for a $10k investment.
For a non-KiwiSaver managed fund, it is 1.23 per cent, or around $123 a year, for a $10k investment.
But Claire Matthews, a KiwiSaver expert at Massey University, said she expected only a small number of over-65s to sign up.
"A lot of those people aren't employed. They have already got their finances set up."
She was also cautious about people moving their money from term deposits into KiwiSaver.
"It is important they have enough information and advice to understand the risks and ensure it is right for them in terms of their goals."
She said it could also potentially have a detrimental impact on the rest of the managed fund industry.
"Not because I would expect people to move their money into KiwiSaver, but because it will reinforce people staying in KiwiSaver."
That could mean more people leave their money in KiwiSaver rather than moving it to other managed funds.
The other change from Monday is that new members will no longer be locked in to the scheme for five years.
Members between the ages of 60 to 64 (inclusive) who enrol on or after July 1, 2019 will be able to withdraw their KiwiSaver funds at 65.
But they will also miss out on getting the government contribution for a minimum of five years.
Hawes said he was happy for the change to come in as people getting both the KiwiSaver government contribution and New Zealand Superannuation were potentially double dipping.
But Matthews questioned the need to change it.
"I don't think it was a major detriment."
She said given the high membership of KiwiSaver, most people would probably be in it for more than five years by the time they got to 65 and the change was more to make administration easier.