At what point can someone call themselves "a writer?"

Is it

1. as soon as they decide they are going to write something?

2. when they are in the process of writing something?

3. when they have something published / optioned?

4. when they are earning a living from something they have wrote?

I am interested in finding out your opinions

I'm going with (2).  Thinking (1) is cheap: I think of things I might do a dozen times a day.  Very few of them come to anything.  And (3) is a goal many people I would consider writers never reach.  This is a very tough industry - you can be really quite good and never break into it.  As for (4), this is extremely rare.  Many quite well known writers need a "proper" job to make ends meet.  Few of us would care to be our family's breadwinner on the uncertain rewards a writer can expect.

But hope springs eternal.  Get writing, and see what happens.

I agree with Jo. If you write, you're a writer, whether it is for fun or aspirational.

When one decides, or seemingly is desirous of writing something, that is not a writer, that's a priliminary state...The most important step for one is to, get out the bed, grip that pen and paper, remove the digital objects aside, cause they are distractions and obstacles, and to sit intently by censuring your wisdom, and just go on.
Number 2 is the best fit, it doesn't matter if you aren't publishing, or marketizing and commercializing, but what matters is, if you have the will, wit and mind to just write something, be it life-changing, or a play in the mud, it is not a matter.
To write, is to carve out your imaginations and thoughts, and a writer is not just someone whose profession and passion is writing, but whose all arc, existence and belief is TO WRITE. God, even Rene Descartes said, "I think, therefore I am", so grant that, and writing isn't just for money's sake, but to pour your heart into something, as long as you're happy :)