"I don't know," Cyrus said. "As I was writing the book, I wanted to keep that particular moment as open-ended as possible because I didn't know the answer. They're young, they're kids. The great news is they're great friends. They're really, really good friends. If you end up getting married, that's your business."
Tabloid rumors have been swirling in recent weeks that the young couple is splitting up.
"I play it by ear, and I know whatever is meant to be, that's the way it's going to happen," Cyrus said. "I don't tell anybody how to live, anybody. I say, 'here's what I've done,' and I'll mostly preface everything with, 'the only thing I do know is I'm not sure I know anything, so take it with a grain of salt.'"
Cyrus wrote a song about Miley called, "Ready, Set, Don't Go," which was released in 2007. In the song he talks about his daughter growing up and moving on without him, but wouldn't go as far as to say she was growing up too soon.
"How do you judge in this world what's too fast, what's too slow," he said. "You look at teenagers, everything, everything in this world, what exactly-- how would you make something perfect?"
In the past, Cyrus has been accused of pushing his daughter -- a former Disney star turned racy pop icon -- into the spotlight too early and too fast. It's something Cyrus denies.
"When you get into the entertainment business ... Kris Kristofferson said to me one time during the midst of, you know, some of the stuff," Cyrus said. "He said, 'Hey hoss, just remember, man, the turkey with the longest neck is the one everybody is shooting at.' That's poetry, man. It's true."