The Irish Fiscal Advisory Council (IFAC) has warned that Ireland will soon become one of the fastest ageing populations in the EU.
In its first Long Term Sustainability Report, the council said the impact on government debt will be "substantial" and "long-lasting".
The percentage of the population aged 65 and over, compared to the numbers aged 15-64, will more than double from 22% today to almost 47% in 2050.
This means relatively fewer people working to sustain higher spending on healthcare and pensions.
IFAC warns in its report today that spending to keep up with an ageing population will push the public finances into deficit from 2026, adding substantially to the national debt over time.
The decision to defer next year's increase in the pension age to 67 will add €575m to current spending and rise over time, something its acting chair Sebastian Barnes describes as "a step in the wrong direction".
The cost of not increasing it to 68 in 2028 as planned will add another €1.5bn a year.
Mr Barnes said that policy action will be required in the coming years to manage the impact of an ageing population on pensions costs and more widely to manage pensions and health pressures.
"Prompt and early action in the coming decade will help to reduce the overall adjustment needs," he said.
"As life expectancy increases, implementing already legislated increases in the pension age to beyond 66 will go a long way to achieving this."