Applicants must be a minimum of 17 years of age on day of entry; however an age waiver may be sought for Army applicants entering the ADF through ADFA at 16 years of age.
Maximum age on entry is 50 years of age for 3 year degree studies and 49 years of age for 4 year degree studies. Maximum age guidelines are set to ensure 

ROYAL MILITARY COLLEGE DUNTROON

Must be aged between 17 and 53. Applicants will not be allowed to enter the ADF until they achieve a minimum of 17 years of age, however they may be able to initiate the application process from 16 years and six months of age, depending upon the capacity of their local recruiting centre.

OFFICER (RESERVE)

Applicants must be aged between 17 and 54 years of age inclusive on entry. Applicants will not be allowed to enter the ADF until they achieve a minimum of 17 years of age, however they may be able to initiate the application process from 16 years and six months of age, depending upon the capacity of their local recruiting centre.

CITIZENSHIP REQUIREMENT

AUSTRALIAN DEFENCE FORCE ACADEMY, ROYAL MILITARY COLLEGE DUNTROON

Only Australian citizens are permitted to serve in the ADF. If you are a Permanent Resident of Australia, the ADF may consider a temporary waiver of the citizenship requirement if the position for which you are applying cannot be filled by an applicant who meets all the citizenship requirements, and then only in exceptional circumstances. You will be required to obtain Australian citizenship as early as possible following enlistment or appointment.

SECURITY REQUIREMENT

AUSTRALIAN DEFENCE FORCE ACADEMY, ROYAL MILITARY COLLEGE DUNTROON, OFFICER (RESERVE)

The Department of Defence requires ADF employees to have security clearances appropriate to their employment. A process of background checks, collection of relevant information and, as required, interviews, enables the Australian Government Security Vetting Agency to make an informed assessment of an applicant's suitability for a security clearance.
The minimum security clearance level required is Negative Vetting Level 1,
current policy requires applicants to have a checkable background for the previous 10 years. 

APTITUDE REQUIREMENT

AUSTRALIAN DEFENCE FORCE ACADEMY, ROYAL MILITARY COLLEGE DUNTROON, OFFICER (RESERVE)

The application process to join the Australian Defence Force requires you to complete a series of aptitude tests including verbal, spatial and numerical ability and a general maths test. 
Psychology support staff will explain what is involved with each test. The aptitude tests provide information about your suitability for the Defence Force and for particular jobs. Defence Force Recruiting can then help you identify jobs that best match your abilities.

To be eligible for admission to UNSW@ADFA, applicants must have completed Year 12 and obtained an entrance rank high enough to qualify for entry to the relevant degree program.

Assumed Knowledge Requirements is the level of subject knowledge that a lecturer or a tutor of a first year UNSW@ADFA course could reasonably expect of students enrolled in that course. Assumed Knowledge is fundamental to the assessment of whether or not an applicant is likely to succeed and is taken into account by the ADF (during the recruiting process) and by UNSW@ADFA when assessing the application.

People wishing to apply for the Military Police must be a minimum of 17 years of age with a maximum of 53 and must be born or have obtained an Australian citizenship. Applicants must also pass a series of tests and that will assess their verbal, numerical and spatial ability as well as physiological evaluation as well as physical tests and medical evaluation. Along with this a series of background checks and interviews to assess if the person is suited for the position. Applicants must also have completed year 12 of high school and have received the minimum ranking high enough for their desired field.