Sydney and Melbourne will each house 7 million people by 2060; Australia might house 42 million. By then 58 per cent of the population will be in their 50s or older, and importantly 51 per cent of the voters will be that old.

Australians aged 65 and over will account for one quarter of the population. One in six Australians will be aged 75 or more.

Ageing population: It has been predicted that by 2060 Australians aged over 65 will account for one quarter of the population. Credit:Greg Newington

Even the very old will become more numerous. A Productivity Commission research paper - An Ageing Australia: Preparing for the Future - to be released on Friday says at present Australia houses one person aged 100 or more for every 100 babies in their first year of life. By 2060 there will be 25 centenarians for every 100 babies.

The commission comes up with the projections by reworking what it believes are "seriously misleading" Bureau of Statistics projections. Whereas the bureau thinks a girl born today can expect to live to 84, the commission thinks she will live to 94 years.