Miley Cyrus became famous as a Disney child star, but it's her very adult behavior in her teenage years that has put her in the headlines recently, from flaunting her slimmed-down body in provocative clothes to becoming engaged to Australian heartthrob Liam Hemsworth at the age of 19.

Now the former "Hannah Montana" star is fighting back against critics who say she's too young to wed 22-year-old Hemsworth, telling Marie Clare magazine the pair's love is not reckless.

"Me and Liam both have been together a really long time, and I just know that this is what I want … for my life," she told the magazine. "Life is too short to not spend every moment making the person who makes you the happiest happy in return."

Cyrus and Hemsworth met in 2009 while co-starring in "The Last Song," a movie about two teens who fall in love.

Appearing as the magazine's cover girl, Cyrus said fans and naysayers should not expect her to walk down the aisle anytime soon, or necessarily in a grand way.

"I don't really care about the wedding or the piece of paper as much as I do the promise we've made to each other," she said. "And we want to have a long engagement."

Cyrus said she was completely surprised when Hemsworth, star of the "Hunger Games" and her boyfriend of three years, proposed to her in June at the Los Angeles-area home they share with their five dogs.

Cyrus told Marie Claire she had pointed out the engagement ring, a 3.5 carat cushion-cut antique diamond by celebrity jeweler Neil Lane, to Hemsworth but didn't know that he was planning to propose.

"We'd been kind of talking about [getting engaged], and I saw something like it online at one point and thought it was really pretty," Cyrus said. "But I usually wear rose gold. I just love that it's old and has a story. And I'm happy, because it doesn't look like anything else I wear."

Also surprised by the engagement were Cyrus' parents, Billy Ray and Tish, whom, Cyrus reveals, Hemsworth did not ask permission of ahead of time.

Even so, Billy Ray Cyrus took to Twitter after the news broke in June to say, "All I ever hoped for as a daddy was to see my kids reach their dreams. To find happiness … peace of mind … and someday know … true love."

It's a good thing they all get along, considering their living situation, which Cyrus also details in the interview.

Cyrus and Hemsworth now live in the Cyrus family's 8,000-square-foot Mediterranean-style villa in the San Fernando Valley. Her parents have since relocated two houses down from them.

"It's really weird [sleeping] in my parents' room," Cyrus said. "Now it's my room, and Liam is at my dad's sink, and I'm at my mom's."

"It's really strange, but also really cool," she said of the accommodations. "The first time I ever met or hung out with Liam was here. When he first moved to America, he didn't have any family here, so our family became his. This is where all our memories are being made."

Along with the new ring, new home life and a new, shorter blond hairdo, Cyrus is also sporting a trimmer physique, which she has not hesitated to flaunt on Twitter and the red carpet.

"I've gotten a little more comfortable with my style, and I think that's being comfortable with who you are and [your] sexuality," said Cyrus, who credits Pilates for her washboard stomach and leaner look. "I've gotten more comfortable with that."