South Australia has one of the oldest populations in Australia, with a median age of 40 years in 2018.
But age structures and settlement patterns differ across the State - some areas are younger, and some are older.
This blog looks at the recent release of ERP data by age and sex, with a focus on South Australia and the mining community of Roxby Downs.
In 2018, Australia's median age was 37.3 years.
This means half the population was younger, and the other half older ie it is the midpoint.
Australia has an ageing population but the median age only increased marginally between 2013 (when it was 37.2 years) and 2018.
Higher levels of overseas migration are adding more young people to the population, which has the effect of pulling the median age downwards.
On the measure of median age, Tasmania is Australia's oldest state.
In 2018 the median age was 42.3 years.
In South Australia it was 40.0 years, followed by NSW with 37.5 years, just above the national figure.
The youngest state was the Northern Territory (32.9 years).
South Australia was the second of Australia's states to record a median age of 40 years, a milestone reached in 2017.
In 2018, 16.7% of the population (around one in six) was aged 65 years and over.
South Australia's population growth is modest and the demographic processes tend to reinforce the ageing population.
For example, there is a long history of interstate migration losses - the last time there was an annual net migration gain was back in 1990-91.
In addition, the level of natural increase has trended downward this decade, indicating the difference between the number of births and deaths is declining.
However the median age varies considerably across the state.
The map below shows the median age by LGA for 2018.
In general, LGAs in Adelaide have a lower median age, but many parts of coastal and rural South Australia are much older.
Outback South Australia also tends to be younger, influenced by the higher proportion of Indigenous persons, and in some areas, the mining workforce.
The LGA with the youngest median age is Anangu Pitjantjatjara Area Council (aka APY lands), an Indigenous area in the State's northwest.
The median age here was just 28.4 years.
The oldest median age was recorded in Victor Harbor, on the Fleurieu Peninsula (57.8 years).
This has long been a retirement and holiday destination, with good transport connections into Adelaide.
There were 13 LGAs in South Australia with a median age of 50 years or more, including all of the Fleurieu and Yorke Peninsulas, as well as parts of the mid-North and Murraylands.
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While the median age can be an indication of how old a population is, it can also mask elements of the age structure.
From a service planning perspective, the composition of the age structure is an important indicator of the demand for particular services.
The small outback community of Roxby Downs illustrates this point.
This is a remote mining community located near the Olympic Dam Mine in the northern part of South Australia.
In 2018, the population was just 4,014 and the median age was 31.7 years - one of the lowest in South Australia.
In common with many mining communities, there was rapid growth during the peak of the mining boom.
The population peaked at 4,826 in 2011, but declined thereafter, but has been relatively steady since 2016.
A proposed expansion of the mine is likely to see the population increase again in the future.
Because it's a mining community, not only is the age structure dominated by those of working age, but the sex ratio is quite high, at 132 males per 100 females.
The number of males outnumbers females in most cohorts, particularly those of working age ie 20-64 years.
The age and sex structure of Roxby Downs Council is shown in the graph below.
Almost three-quarters of the population are aged 15-64 years, and a further 26% are aged 0-14 years.
Despite the high sex ratio, there is a large proportion of family households.
There are very few people in older age groups, with less than 50 people (1.2% of the population) aged 70 years or over.
This is not a place where people stay once they are no longer in the workforce - the antithesis of a retirement destination.
In addition to the age and sex structure, Census data shows that the mining industry accounts for half of employment in Roxby Downs, and around two-thirds of households are rented (which is linked to higher rates of household mobility).
The decline in the population is driven by out-migration, primarily of working-age people.
These factors combine to create challenges in providing services for a small, remote and transient population.
In 2018, the median age of the South Australian population was 40 years, compared to 37.3 years for Australia.
The older median age is a result of long term demographic trends which have reinforced an ageing trend, such that one in six South Australians are aged 65 years and over.
The small outback LGA of Anangu Pitjantjatjara recorded the lowest median age (28.4 years), and the oldest was Victor Harbor (57.8 years).
The median age can mask elements of the age structure that are important for service planning.
This is illustrated by the mining community of Roxby Downs, where the population is dominated by people of working age, but it is a transient community which creates challenges for service planning and provision.