Examining the angry track marks on her pale slender arms, Elle Fanning couldn’t help but smile.

“I know this sounds weird, but it just felt like I’d come of age,” says the actress who gives a haunting turn as a naïve young woman who becomes a revival preacher after being rescued from a bordello in Ben Affleck’s adaptation of Dennis Lehane’s prohibition-era mobster novel, Live By Night.

Co-starring with Sienna Miller, Zoe Saldana and Affleck himself, Fanning’s Loretta Figgis is the subject of the film’s most evocative line, “She didn’t make it to Hollywood, she just made it to Los Angeles.”

“I know, it’s funny that line, there’s several ways you can take it,” laughs Fanning who was just three-years-old when her Georgia-based family moved to Los Angeles to pursue acting opportunities for her big sister Dakota, now 22.

Fanning and Ben Affleck star in the Prohibition Era-set film, which delves into the world of organised crime (Claire Folger/ Warner Bros Entertainment Inc) (Claire Folger/ © 2016 WARNER BROS. ENTERTAINMENT INC. ALL RIGHTS RESERVED)

Unlike her Live By Night alter ego, The Fanning sisters lost little time settling into Los Angeles and subsequently conquering Hollywood.

“So, getting the track marks done every day was a weird experience. Eventually I began wearing them all the time because they were tattoos, and so if I had to come in the next day, I would just wear them to bed, and then when I woke up the next morning, they would still be there. But I had to remember to wear long sleeves when I went out. I didn’t want anyone thinking crazy things because they looked so real.”

Dressed in white gossamer dresses, she strikes an ethereal presence maturing over several years in Live By Night.

“This felt like my most mature role. Im not just playing the kid anymore, I’m finally a young woman. Now that I’m 18, it matched up to the place that I’m at now, feeling like I’m on a cusp where I’m not quite an adult, but you’re treated more like one,” says the actress who has grown up before our eyes on screen, just two-years-old when she played a younger version of her sister Dakota’s character in I Am Sam with Sean Penn, graduating to cute kiddie movies Daddy Day Care and Because of Winn-Dixie whilst featuring in dark adult films including Reservation Road with Joaquin Phoenix and Alejandro Inarritu’s Babel.

Only ten years old when she really hit her stride, she appeared as the younger version of Cate Blanchett’s character in David Fincher’s The Curious Case of Benjamin Button followed by more age appropriate fare with Super 8, We Bought a Zoo and as Aurora in Maleficent.

Fanning in Nicolas Winding Refn’s thriller ‘The Neon Demon’ – the role she claims is her most risky to date

Unlike many child actors who are either deeply jaded or in rehab by time they hit their late teens, Fanning retains an almost child-like enthusiasm for what she does. “I think I’ve just always kept the fun, even if that word is over-used, but it’s true. If you’re not having a great time and loving it still, then you should do something else. Everything still feels fresh for me – every new character, new script, new environment, and I still get very excited by it.

“I love a risk. If something seems impossible, then that’s what I want to try. That is my motto in many ways. I try to pick things that are very different from each other so that I’m in different places all the time. It strengthens me and makes me grow,” says the actress who views her role in Nicolas Winding Refn’s thriller The Neon Demon as her riskiest to date, even skipping her high school prom last year to promote the film at Cannes, her date flying out to recreate their prom on the red carpet.

Still coming to terms with her new adult status, and with none of the usual plans to attend college, she says today, almost eight months after graduation.

“I’m glad I had the experience of going to a totally normal high school. Some of my friends have gone to college, others aren’t, but we are in this limbo where we talk about ‘Oh, we’re not in high school anymore, it’s such a strange thing,’ So you do miss it, but then also you’re like ‘I’m so glad I’m done.’ Right now I‘m just happy I graduated but maybe in a couple of years, I’ll be missing high school. But I’m doing exactly what I want to be doing, so I’m very excited about that.”

If it seems like she and her sister have an uncanny knack for picking interesting material, she credits her mother, former pro tennis player Joy Arrington, for giving her the best advice.

“It usually comes down to my mom. I’m also very close to my grandmother who lives with us as well and used to go with me on all my film sets when I was younger while my mom would go with my sister before she turned 18.

“Also when you make choices, it’s more like ‘Oh, I want them to be good for them’, meaning my family. I don’t really think about it in any other way, so my family’s opinion matters the most. For sure. Always,” says Fanning who still lives at home with her family, including father Steve Fanning, a former minor-league shortstop with the St Louis Cardinals.

In no hurry to leave the family nest, she says, “Because I travel a lot, going back home, and being with my family is always special. I live in the house that I grew up in since I was seven years old, so, being in my own room, with my family right there, is a very comforting feeling.

“I enjoy travelling for work and having my family home makes it easier to go away for long stretches when I know I have them to come home to. It grounds me, and it feels very safe. It’s also very important to have, because you can’t just always be kind of floating, you know,” says the actress who spent the last six months between the UK filming Neil Gaiman’s How To Talk To Girls At Parties and in Louisiana, shooting Sofia Coppola’s The Beguiled.

Remaining close to her big sister, she says, “We’re sisters so of course we do have our moments as you know, like if I steal any of her clothes, that’s not good. But I really look up to her, I mean she’s my big sister. Since she did movies first, I started out because of her so she led the way to that.”

Attending her first Paris runway aged 13, she quickly became the face of Marc Jacobs and still enjoys promoting designers on social media. When we meet today in West Hollywood, she’s wearing a silk lilac confection by Vivetta. “I love fashion because I can turn into anyone I want to be,” she says, those bright blue eyes widening with enthusiasm. “I got this dress from Vivetta because I have a shirt of theirs that I loved and wore on Instagram so then they sent me some clothes.”

Fanning says her character in ‘Live By Night’ is her most mature role yet (Claire Folger/ © 2016 Warner Bros) (Claire Folger/ © 2016 WARNER BROS. ENTERTAINMENT INC. ALL RIGHTS RESERVED)

Debuting her public Instagram account on her 18th birthday last year along with her first selfie and a birthday cake, she takes her fashion choices seriously. “It’s not just a petty thing. Like the fashion industry is a whole industry so I enjoy being a part of that.”

Part of her charm lies in a stubborn refusal to adopt the airs and graces of an older person, readily giggling as phrases like “totally cool” and “freaking out” spill from her lips.

Considering she only has only a minor role in Live By Night, her Loretta Figgis is a powerful presence, carrying many of the film’s best lines such as, “This is heaven. Right here. We’re in it now.”

The sentiment particularly resonated with Fanning who, together with her sister, attended daily chapel services at Campbell Hall Episcopal school in North Hollywood and whose family are members of the Southern Baptist Convention. “We’re all living on this earth so it’s what you do now, from the start to the finish and all the in between, that matters and what is going to make you feel the most fulfilled,” she muses. “It’s right here in this moment that you have to seize it and do what you want.”

Borrowing from the film’s title, she surprisingly reveals an affinity for night-time, preferring the dark shadows to the bright California sunshine. “I am definitely a night person. I stay up very late. It’s hard for me to go to sleep early. I feel safe at night. The darkness makes you feel comfortable in a way. Also maybe, there’s a hidden aspect to it, where you feel that you can kind of sneak around. I don’t know, I just prefer the night to day.”