The latest projections from the ARC Centre of Excellence in Population Ageing Research found Australia's overall population is likely to reach 32 million by that time.
About 6.6 million of that figure will be people aged 65 and over, an increase of 54 per cent from current figures.
"We are assuming that long-running trends in declining mortality will continue - more and more people are surviving to older ages," report author Dr Tom Wilson told AAP.
"We've also got more people coming up to the older ages because of the increase in births from many decades ago."
Tasmania and South Australia will have the largest group of older residents, with those aged over 65 accounting for 26.3 per cent and 24.1 per cent of their respective populations in 2041.
Australia's centenarian numbers are expected to climb by 200 per cent over the same period, with 15,900 people expected to be aged 100 or over in 2041.
"That's the population that tends to need more medical care and aged care," Dr Wilson said.
"Hopefully this provides useful background information for people who are looking into aged care workforce needs, medical care, and the economic implications of all of this."
The latest projections show 20.8 per cent of Australia's overall population in 2041 will be aged 65 and over, compared to 16.8 per cent this year.
"Compared to most developed countries, that's low," Dr Wilson said. "Most developed countries have way bigger shares of population in the 65 and over age groups.
"It shows that Australia is still a relatively young country."
After years of slow population growth due to COVID-19 border closures and halted migration, Australia's population will begin to bounce back in the coming years.
From next year onwards, more than 300,000 people are expected to be added annually to Australia's population.
NSW will continue to be Australia's most-populous state, with a projected growth to 9.64 million people over the next two decades.
PREDICTED 2041 POPULATIONS FOR AUSTRALIA'S STATES AND TERRITORIES:
* NSW: 9.64 million (from 8.09 million in 2021)
* Victoria: 8.41 million (from 6.55 million in 2021)
* Queensland: 6.79 million (from 5.22 million in 2021)
* Western Australia: 3.61 million (from 2.75 million in 2021)
* South Australia: 2.07 million (from 1.80 million in 2021)
* Tasmania: 622,000 (from 568,000 in 2021)
* ACT: 589,000 (from 454,000 in 2021).
* Northern Territory: 300,000 (from 249,000 in 2021)
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