Can I use it as a form of identification when I go clubbing or something so they know I'm over 18?
Unfortunately no. An ASIC can be issued to a person under 18yrs, the only difference being that they are not subject to a security background check.
Ironically, despite all the documents we have to produce to prove ID and operational need, the ASIC itself is not a recognised form of ID for things like 100 point checks at banks etc.
Getting back to KALAVO's point, I would goto the Council or corporation that controls the airport and ask to see the plan for airside/landside boundaries. If you hangar is landside inspectors have the right to walk in but you are not required to display an ASIC.
Quite simply, it is determined by where the airside signs are located. If on the outside of the hangar - landside, then all of the hangar will be designated as airside. If the hangar is exempt, then the signs will be on the inside doors exiting to the airside area. All operators of the airports will be Aviation Industry Participants under the relevent airport's Transport Security Program (TSP) and as such should have a copy of that document which will show plans or drawings of these areas.