A new paper by the Australian National University was published on Thursday, revealing the first public estimates of the growth of this cohort of NDIS participants in the first 10 years of the scheme's operation.

It forecast a five-fold growth in the number of over-65 participants in the scheme, reaching about 100,000, up from current levels of about 18,200 such participants.

There are currently only about 75,000 approved participants of all ages in the scheme, but early forecasts indicated the total number of participants could reach up to 500,000 over the decade to 2026.

That growth was largely due to existing participants getting older, as most people with a disability must be approved plans before they turn 65 years old to access support under the scheme, instead of aged care.

The research showed the estimated 8000 men and 10,200 women aged 65 or older in the scheme in 2017 would grow to 48,800 men and 56,900 women by 2026.

The massive growth in all, but particularly older participants, would have longer-term implications for the federal and state budgets, given it could affect the budgets for the NDIS and aged care systems at both levels of government for years to come.

It follows the Turnbull Government raising the Medicare levy from two per cent to 2.5 per cent from July 2019 to "fully fund" the scheme.

After Opposition pressure over the impact of the levy rise on low income families, Treasurer Scott Morrison this week tabled a bill to exempt some two million Australians from paying the extra .5 per cent - including individuals earning up to $21,000-odd and families earning up to $36,500-odd.

It is unclear if the proposed levy increase will keep pace with the rising pressure from growing numbers of participants over the longer term.

ANU Professors Nicholas Biddle and Heather Crawford wrote that disability services were also likely to be used with greater intensity by older people, increasing the overall costs of service provision.

"Rates and severity of disability increase substantially with age, so as populations age governments will be challenged to provide disability-related services to an increasing share of the population," the paper reads.

The research looked not only at rates of transitions - people moving from mild to moderate and severe disability categories - as well as estimated population growth and potential mortality rates among those people with severe disabilities with higher mortality rates.

Prof Biddle and Crawford also assumed existing participants would stay in the scheme after turning 65, rather than moving into the age care system.

But, if the opposite happens, they wrote it would be "a strong indication that for some the NDIS is not meeting their needs".

The research was funded by the Department of Social Services and an "unpublished confidential report" was provided to the federal government in July 2014, but a public version of the report was only published in the Australasian Journal on Ageing on Thursday.