In the pub scene when they are about to leave for Gallipoli there are flags on the wall of the Allies - France, Britain, and Australia. There is also a flag of the United States. The battle of Gallipoli occurred in 1915, but the United States did not enter the war until April 6, 1917. It was neutral in 1915, and traded with both the Allied and Central Powers.
When the young Australians ride the donkeys past the two British officers under the archway, in the first shot, looking behind the officers, there are three of them. In the next shot, looking to the front of the officers as they ride past, there are suddenly four on donkeys.
The movie opens with young Archy Hamilton running a 100-yard practice sprint at dawn, with his uncle keeping time with a stopwatch. After Archy finishes the race, his uncle shows him the watch and Archy's time is just under 10 seconds (9.58 seconds). If one times Archy's sprint, however, it actually consumes about 15 seconds of screen time.
The fourth wave in the attack at The Nek did not start at the the insistence of senior officers. The attack was called off after the third wave, but about half the 150 men in the fourth wave attacked without orders.
In the movie it is stated that a person had to be 21 years old to enlist. According to the Australian War Memorial website for enlistment, in 1914 the age requirements were 18-35 years old, and in 1915 the age requirements were 18-45 years old. However, enlisting below the age of 21 required permission from parents or guardian.
When the ANZAC artillery begins firing on the Turkish trenches just before the climatic battle scene, the guns do not kick back and some have bits of rust around the muzzle edges which indicate that the artillery pieces are not operational weapons at all for they are just popping white smoke out of the muzzles with the camera violently shaking to simulate the guns being fired.