How does an 18 year old become a terror suspect...?

[Lenny]

How tough it must be to spend your life subjected to abuse, sideways glances, misunderstanding, just because of what you wear, what you believe or what you look like.
Muslim, Sudanese, Aboriginal, even transgender youth to name just a few. How exhausting and demoralising to know that so many people have you summed up before you even open your mouth. Enough to make you want to give up before you even try. For some, their parents have probably been through the same, or even some worse form of hell. No wonder you want to stick together with those who understand what it's like. No wonder you are angry and feel shut out, different, unwanted, misunderstood. Paradise lost.

[onthefly]

Remove the terror label, and I would have assumed disaffected youth with mental health issues. The other stuff may or may not be relevant.
I would say probably the greatest terror threat suffered by Australians day to day is domestic violence.

[nothing2lose]

Same same but different...

Robina shopping mall 'gunman' meant to kill: court