SHE may not be old enough to drink or vote, but Chloe Grace Moretz is already a veteran in Hollywood circles.

The ambitious teenager is also a bit of a wise soul.

The 17-year-old actress burst on to the movie map with her scene-stealing role as Hit-Girl in 2010's Kick-Ass which, along with her starring role in Let Me In, landed her on Time magazine's prestigious Top 10 Movie Performances of the Year list.

She's a girl who takes her craft seriously and deems the increasing paparazzi interest in her "kind of silly".

She has been spotted in public with David and Victoria Beckham's son Brooklyn, but she's tighlipped on her personal life.

"It's annoying that people care more about what you wear or who you're with. It seems a little antiquated. I think the only thing they should care about is whether you're a good actor," says Moretz, who hails from Atlanta, Georgia.

And while her fame grows, who she can trust shrinks.

"There are things that come out and it says, 'A source close to the person...', and I'm like, 'Who?'"

She's found a "sneaky but fun" way of weeding out the culprits - by telling people she suspects fake stories, and seeing if they end up being reported.

"When they get out, I'm like, 'Yes! You're a rat and I knew it!'," she says, adopting a Deep South accent and clicking her fingers with mock attitude. "So I don't really trust anyone any more - besides my close family."

She describes her relatives as "really loud and crazy - they're wild". Not unlike the family of Mia, her character in new movie, If I Stay.

Based on the bestselling young adult novel by Gayle Forman, her father is the drummer of a punk band, her mother reveres women like Blondie's Debbie Harry, and Mia, meanwhile, wants to play the cello at prestigious Juilliard arts school.

"I was able to understand Mia on a deep level, because I discovered acting when I was five and she found the cello when she was eight, so we both have this innate thing that happened to us where we found our passion early on," says Moretz, who also starred in 2005's The Amityville Horror opposite Ryan Reynolds, as well as 2012's Dark Shadows, Hugo and last year's Carrie remake.

One day, Mia's involved in a car accident and, left in limbo, is forced to make a choice - to stay in this world or move onto the next.

Moretz's own views about death are optimistic. "If it means I'm reunited with my grandma, then I think that would be awesome, and it'd make me so happy to see everyone. I welcome it, in a way. Not in a way that I want to make it happen early, but it's not as scary as humans chalk it up to be," she says.

The film is told through flashbacks as Mia reflects on her life, relationships and a time when she believed the biggest decision she'd ever have to face was to pursue her musical dreams or be with the love of her life, Adam, played by British actor Jamie Blackley.

Experiencing love in real life helps when it comes to depicting it on screen, she notes. "But there are many forms of love and it's not an easy thing to fabricate," adds Moretz who, like Mia, is attracted to people with "ambition and a drive for something".

"When you're younger, you don't have any boundaries, so you give everything. Then you realise you've no more ," she says with the air of someone at least twice her age. "It becomes this tainted, crazy amalgamation of trauma and emotion, and when you grow up, you realise there are pieces of yourself that are just for you. It's hard, at a young age, to understand that."

She has no interest in depicting someone without substance. "Even when I was younger, I never liked auditioning for the role that just involved being the little girl. Even now, I read these scripts about these girls where they're going, 'Oh save me!'," she continues. "I can't wrap my head around it and it annoys me.

"It's why I love Mia so much, because she doesn't say, 'I'll give up Julliard for you'. She contemplates it for a second and then she's like, 'No, why would I ever give up what I love, what I've given my life to?'"

Before cameras rolled, Moretz spent time studying cellists and noticed many were introverted until they began to play. "It was fascinating to watch them transform before my eyes. They become so animated and so passionate."

In the months before filming started, R.J. Cutler, the director, ensured Moretz always had access to a cello wherever she was in the world.

"I'd come to these new locations and there'd always be this instrument lurking around, following me," she recalls, laughing. "From Leipzig in Germany to the middle of Louisiana, the hotel staff would give me a strange look and say, 'Ma'am, there's a cello for you downstairs'. But actually, living with it constantly made a difference. For cellists, it really is an extension of their body."

According to her teacher, she was a natural. "She did tell me I had good strength with my fingers, but I'm not sure whether she was buttering me up."

l If I Stay is showing in cinemas now