 The recruitment process was managed by the various military districts . At the outset it had been planned to recruit half the AIF 's initial commitment of 20 @,@ 000 personnel from Australia 's part @-@ time forces , and volunteers were initially recruited from within designated regimental areas , thus creating a linkage between the units of the AIF and the units of the home service Militia . In the early stages of mobilisation the men of the AIF were selected under some of the toughest criterion of any army in World War I and it is believed that roughly 30 percent of men that applied were rejected on medical grounds . To enlist , men had to be aged between 18 and 35 years of age ( although it is believed that men as old as 70 and as young as 14 managed to enlist ) , and they had to be at least 5 feet 6 inches ( 168 cm ) , with a chest measurement of at least 34 inches ( 86 cm ) . Many of these strict requirements were lifted later in the war , however , as the need for replacements grew . Indeed , casualties among the initial volunteers were so high , that of the 32 @,@ 000 original soldiers of the AIF only 7 @,@ 000 would survive to the end of the war . 
