CANBERRA, Dec. 20 (Xinhua) -- The age of Australia's population is on the rise, data released Thursday from the Australian Bureau of Statistics (ABS) revealed.

According to the ABS, 15.7 percent of Australia's population was aged 65 years and over as of June, up from 12.2 percent in 1998.

The data revealed that the island state of Tasmania was home to Australia's oldest population, with 19.7 percent of its people aged 65 and over.

"Over the 20-year period to 2018, the proportion of Australia's working age population remained fairly stable at around two-thirds of the total population, while the proportion of people aged 65 years and over increased from 12.2 percent to 15.7 percent," Anthony Grubb, ABS director of demography, said in a media release on Thursday.

"Conversely, the proportion of people aged under 15 years decreased from 21.0 percent to 18.8 percent during this same period.

"There are several drivers for Australia's ageing population -- more of the large baby boomer cohort is reaching 65 and there has been an increase in life expectancy. This has occurred alongside low fertility rates which have resulted in fewer children.

"Tasmania continues to have our oldest population, with a median age of 42 years, while the Northern Territory is still the youngest with a median age of 33 years."

Australia's population grew by 390,500 in the 12 months to June to 24.9 million.

Net overseas migration added 236,700 people to the population, or 61 percent of the total growth.

There were 161,000 deaths and 314,800 births in the period, resulting in a natural population increase of 153,800.