The Australian Bureau of Statistics Regional Population by Age and Sex 2020 report released Friday showed the median age in capital cities was 36.5 years on June 30 last year - an increase of 0.4 years from the year before.

"That doesn't sound huge but 0.4 for a year was our biggest increase in age for the capitals on record," Australian Bureau of Statistics demographer Andrew Howe said.

The median age in the capitals had remained at 35.9 years between 2014 and 2018 after a decrease from 36.1 years in 2011.

This compared to an annual increase of 0.2 in regional areas to June 30, 2020, when the median age outside the capitals hit 41.4 years.

"There's still a long way to go but the gap between the capitals and regions got a little bit closer last year," Mr Howe said.

The data range included the first quarter of the pandemic and Mr Howe said he believed the sharp drop in international migration from closed borders had played a part.

"Migrants are generally younger than people who are already in Australia so migration helps to keep the population younger," he said.

"From a regional perspective, because more overseas migrants arrive in capital cities, it means that the capital cities have historically been younger than the regional areas.

"But because we've had this slowdown in migration, we've seen the capital cities start increasing their median age."

Meanwhile, Canberra had the two youngest areas in the country. Acton (21.6 years) and Duntroon (22.3) topped the list thanks to large populations of students and military personnel. Ninety-nine per cent of the population in Duntroon was aged under 65, men outnumbered women by more than two to one.

On the other end of the scale, at 63.4 years, the retirement area of Tea Gardens-Hawks Nest had the highest median age of any statistical area in the country. The area's median age grew by 0.7 in just two years, with more than 46 per cent of the population being 65 years or older.

*Areas with a population of less than 2000 were not ranked.