The 29-year-old, who split from on-off partner Jude Law in February, explained that she is ready to move on to a more "serious" decade.
She told the Herald Sun: "I think, if you put a camera in anyone's life and document it daily from the age of 21 to 27, there are going to be things that aren't always pretty. I feel as though I experienced my 20s in all their glory and all their disastrousness. Now, I'm much more calm. It feels like a new, more serious decade.
"Things just come out. I'll say the most inappropriate things at the most inappropriate time to the most inappropriate person. Always. I can't wait to be seen as a woman. But I know I probably have to contribute to that with behaviour."
However, Miller admitted that living in Los Angeles means that she still feels pressure to look young.
She added: "Recently, I found myself thinking, I'm getting wrinkles. And things are wobbling, I should go to the gym. Then I was like, f**k it. That's not where the focus should be. Los Angeles is a nightmare for that. I say, people should be young and then be old."
Miller was recently awarded £100,000 in damages from the News of the World.