Hi FlyingCharlie01- defencejobs.gov has the information on height requirements for a Class 1 medical :
Additional Requirements | Pilot - Defence Jobs Australia
They state a minimum height of 163 cm is required, that said I know several people who were told their sitting height was too tall to apply for Army, yet they are now wearing DPU flightsuits.
My advice is to start studying to get the best grades you can, play some team sports, join Cadets or Volunteer Fire Service and look at getting some leadership experience.