Cars don't have the same restrictions.  Guns do.  

How old do I have to be before I can be issued a Firearm Licence?

Under Section 10 of the Firearms Act the minimum age for the issue of a licence or permit in Western Australia is 18.

However, there are no age restrictions on the use of a firearm, other than a handgun, while under the direct supervision of the licensed owner of the firearm.

So any kid can go hunting with dad.

Seeing that you are so interested J here is some light reading for you

http://www5.austlii.edu.au/au/legis/tas/consol_act/fa1996102/

And once you have digested that rere the proposed ammendments

http://www.parliament.tas.gov.au/bills/pdf/3_of_2015.pdf 

A bit of light reading in case you get bored 🙂