I tend to look at this quite pragmatically:
- I write, therefore I am a writer
- I think I can write, therefore I am a writer
- I know I'm a writer, therefore I don't need anybody else to tell me I'm a writer
How about you: Do you have a different approach? Are you a writer? Are you waiting to pass a particular milestone, or meet a certain goal/point on a yardstick, before you call yourself a writer? Do you refer to yourself as an "Aspiring Writer" (which implies you're trying to be, but are not yet, a writer)?