Signs that you are no average 18 year old: You describe having to pay taxes as a "bummer", pride yourself on having behaved "professionally" since the age of six and get career advice directly from Oscar-winner Julianne Moore.

This is why actress Chloe Grace Moretz often comes across as 18 going on 35 in interviews, especially when she talks about having to work extra hard because she is female and not being able to take a break because she is afraid of losing her place to another performer.

But the star of the Kick-Ass films (2010 and 2013), where she became famous playing a potty-mouthed prepubescent superhero, says her family keeps her grounded despite it all.

Speaking to The Straits Times and other press in Cancun, Mexico, about her new science-fiction film The 5th Wave, which opens in Singapore tomorrow, the star is poised beyond her years as she faces a barrage of questions.

She expertly links a query about the pressures of being a teenage star to the movie she is there to sell, which is adapted from a young- adult novel about a girl who goes on the run after an alien invasion of Earth.

"It's about a girl named Cassie, who is just your average teen until she is put in extraordinary circumstances," says Moretz.

"She is your typical, ordinary 16-year-old - she doesn't have a hot boyfriend, doesn't excel in sports or school, but is just figuring out who she is and being a teenager."

Like the character - who goes on a quest to save her brother from the aliens - she is defined by her close relationships with her mother Teri, a nurse, as well as her four older brothers, one of whom, Trevor, 28, doubles as her acting coach.

"The only thing that lights that fire underneath her and makes her tenacity go into overdrive is her brother and his survival.

"And I think it's the same thing for me. I'm faced with so many temptations and worries, and too much power and money, and also the horrible everyday problems of being an 18-year-old, and the only thing that keeps me going and grounded is my family. Without them, I couldn't have done any of this or been the person I am now."

As she has done in other interviews, Moretz emphasises that she is nothing like the stereotypical young Hollywood star who shows up to work hungover because they have been partying all night.

"I've been acting since I was six and the first thing my mum instilled in me was professionalism. When you're on set, these are people's livelihoods, so be professional, be on time, don't fool around. Have a good time, but don't waste time.

"So it was never an issue for me, the temptation most people have to go out and get drunk and showing up to work on Monday slightly drunk. Because I've worked for 12 years to be in this position and nothing is worth wrecking what I've built," says the actress, who at 13 already had lead roles in two hit movies, the action parody Kick-Ass and the horror flick Let Me In (2010).

And despite continuing to get top billing in If I Stay (2014), a romance, and Carrie (2013), another horror film, maintaining a foothold in the industry continues to be "an uphill battle", she says.

"Not just as an actor, but also as an actress, and working against the system in general as a woman.

"On top of that, people expect me to fall because of the young women that have been placed before me as bad examples. I have to walk on eggshells to make sure everyone knows that I'm calm and I'm good and I have a good family and I'm in no danger of going crazy," says the teen.

Moretz, who has spoken out against bullying and sexism - and admitted that negative social media comments about her appearance made her feel "fat" and "insecure" while filming Carrie in 2013 - points out that Hollywood can be incredibly damaging to a young girl's self-esteem.

"You have everyone telling you you're not pretty enough or you're too pretty, you're not skinny enough or you're too skinny, and a hundred different reasons why you won't get this role or be successful," she says.

She would be tempted to take a break from acting to go to university, but "if I walk away for four years I give so many people the opportunity to take my slot".

Her edge in this cut-throat business is her work ethic and perseverance, she says.

"I knew that if I worked hard enough at the craft of acting and my characters and sealed the audition, I would book the job, purely on being the best actor.

"Sure, looks can help you book certain roles, but at the end of the day, if you don't have the acting to back it up, you'll never survive."

And although she has modelled for fashion brands such as Max Mara and Aeropostale and always looks impeccably turned out on red carpets, Moretz says she has not fallen into the trap of becoming obsessed with how she looks.

"If anything, I've become more of a hermit - I hardly wear any make-up outside of press events, just tinted moisturiser and some mascara.

"And I mostly wear sweatpants and a T-shirt. I have an old sweatshirt that my brother's boyfriend gave me, I wear that pretty much every day with some Nike leggings. I'm very low key."

The actress is a bit of an exercise fiend, but this is more of a stress- relieving strategy than an attempt to stay Hollywood-thin.

"As I grow up and do more physical parts, I definitely have to keep my shape up, so I work out six times a day, sometimes four hours a day - I have a very heavy workout schedule.

"But honestly, it's become more about my mental health, my workouts are therapeutic because I need to release all my energy, especially when I'm not acting," says Moretz, who reveals she sometimes does not one but two gruelling spin classes at the trendy SoulCycle gyms in Los Angeles. "That's my cardio, it's fun."

In her acting choices, Moretz's strategy is to experiment with different genres and "try a bunch of crazy stuff" while she is young - "and then I can be more serious in the coming years".

The decision to sign on to The 5th Wave, which could potentially become another young-adult franchise in the vein of the Twilight or Hunger Games films, is one such experiment. Like those franchises, it revolves around a heroic young woman.

Moretz believes "these movies are a huge support system for young women in society - I think it's inspiring that young women can see these movies and go, 'That's cool that someone my age and who looks like me can be strong and not back down to society.' "

When it comes to deciding what projects to take, however, her main guiding principle is one that was taught to her by Moore, who played her mother in Carrie.

"She's a second mum to me," Moretz says of the Best Actress Oscar winner for Still Alice (2014).

"I love her so much and she's always been the biggest proponent of trying to make art as well as money. She said not to take a project because you think it's going to make you a ton of money or famous, and that if you can survive without the money, please make it for art.

"Because if you truly love the character and the project, you'll never go wrong. Even if the movie turns out to be horrible, you will at least be good in it. So that's what I try and stick to."

• The 5th Wave opens in Singapore tomorrow.