The ranks of public servants aged 50 and over are growing while the service itself rapidly shrinks around them, according to the latest APS Snapshots data, and young people are growing even scarcer in federal government offices.

The data compiled from the Australian Public Service annual employee census indicates that more than 31 per cent of federal public servants are now over 50, compared to 20 per cent in 2001.

State of the Service data shows some agencies with staffing levels of over-45s approaching 70 per cent while the proportion of workers aged under 25 has nearly halved in the past seven years.

According to the census, which had a participation of nearly 97,000 this year, the two largest groups of employees were those aged 50 to 54 years and 40 to 44 years, each representing 15 per cent of all APS employees.

There was an increase recorded in the 55 to 59 age group, which grew to 10.3 per cent a year later.

Representation of employees less than 25 years old was down again, according to the census data, with just 3.7 per cent of all employees in this age group, down from 6.2 per cent in 2008.

The Australian Public Service Commission has previously attributed the ageing of its workforce to the impact of government policies that encourage older employees to remain in the workforce or to return after taking early retirement.

But a commission spokeswoman told Fairfax Media that although the ageing trend in the Australian Public Service reflected the picture in the broader workforce, more younger people were being hired by the bureaucracy.

"The APSC is working with agencies to improve the way we attract and retain talented employees of all ages," she said.

"In 2015, 46 per cent of ongoing engagements were aged under 30 years and 19 per cent of ongoing engagements were aged 45 and over.

"An incremental growth in older worker representation is common across many Australian employers."

The ageing worker profile in the service was also caused, in part, by the trend of departments to take slightly older graduates into their annual intake programs than had been the case in the past, according to the commission.

"The changes in the younger demographic is, in part, caused by graduate recruits being older than in the past," the spokeswoman said.

"The APS recruits about 1500 graduates each year."

But Public Service Commissioner John Lloyd has a plan, his office said, to use his push for more part-time and casual jobs in the service to ease the older cohort into retirement.

"The APSC is modernising the APS employment framework to support a diverse workforce," the spokeswoman said.

"This includes encouraging agencies to use flexible working arrangements.

"Flexible work and the ability to shift from ongoing to non-ongoing employment can assist with the transition to retirement for older workers."