The state of a noun when it has reached maturity or an advanced level of development.
Pat: Dude, I remember when used to be so tiny, now she's graduating.
Gray: Yeah man, when you met her she was a freshman, now she's full metal.
The state of mind or being in which a person has titanium-clad convictions, will stop at nothing to accomplish their goals, and absolutely lets nothing get in their way of progress. They may also have a strong urge to protect anyone and everyone they can. Someone who is considered Full Metal can also be classified as a badass and admirable person. However, they may display a hot headed nature over some very trivial things, usually over things they may be sensitive about.
He was a very shy and reserved kid growing up, but as he matured he became Full Metal, and now everyone he knows respects him.