Growing up in Estes Park, 17-year-old Casil McArthur gravitated to colorful anime and the cosplay community. Like many other fans, he enjoyed donning pastel-colored wigs as his favorite anime characters and meeting new friends at cosplay conventions.

But the biggest reason McArthur loved cosplay was because it allowed him to be himself before he was ready to share that with the world.

“That’s when I started dressing more masculine, because I could cosplay male characters and no one would be mad at me for it,” Casil said. “What I liked about the cosplay community was that if somebody didn’t know who you were, but they know the character, they would refer to you using the pronouns of that character. It was something that really helped me.”

McArthur is now taking the fashion world by storm as a transgender model.

He started taking testosterone last December. Since then, he said during a recent interview, he’s never been more comfortable in his body.

McArthur, who is 6-foot-1 with piercing green eyes, started modeling when he was a 10-year-old girl under the name Dani Rose, but it wasn’t until after his transition that his modeling career really took off.

“Last year, I stopped (modeling as a female) because it was becoming too much for me. It wasn’t right, and it didn’t feel right,” he said. “I was like, ‘I refuse to model unless I can do male modeling.’ ”

Two weeks after he started taking testosterone, he did a photo shoot with Craig McDean, a world-renowned fashion photographer whose work regularly appears in Vogue and W magazine, for Interview magazine.

Since then, he’s worked with Calvin Klein, Milk Makeup and Yves Saint-Laurent.

Earlier this summer, McArthur shot a 16-page spread for W magazine’s September issue with renowned photographer Steven Meisel. In one photo, he gazes moodily at the camera while reclining on a motorcycle. In another, he’s holding a cigarette, lips slightly parted.

McArthur has faced plenty of obstacles on his way to becoming a sought-after model. Hormone therapy brought an onslaught of physical changes — his voice deepened rapidly, his shoulders widened and even though he had never had skin problems, he got acne from his newly developing facial hair. At the same time, McArthur went through menopause; he remembered waking up one night in the winter in a sweat-soaked bed from hot flashes.

Once he was ready to start modeling again, McArthur had to relearn everything about his craft, from how to pose to how to shake hands. He’s started working out to develop more of a male physique.

“Male modeling is a lot simpler because you don’t have to try as hard, but it’s definitely difficult for male models because they’re always expected to have such strong, muscular and sculpted bodies,” he said. “Personally for me, it takes a lot of dedication.”

It also hasn’t been an easy process getting the female-dominated modeling industry to accept him. He frequently dodges disrespectful questions and deals with misgendering while working.

“It’s super difficult for me not to shake people sometimes,” McArthur said. “While I have patience, it doesn’t give people permission to misgender me or throw my identity under the bus. Because that still happens — people will misgender me and I’ll correct them, and they’ll be like, ‘Well, I’m still getting used to it.’ And it’s like, ‘No, I’ve been this way for awhile.’ But I’m an open book; people can ask me any question, as long as they’re respectful to me.”

At this point in McArthur’s transition, he easily passes as male. But he still gets anxiety about people noticing his chest bindings when his shoulders are exposed. He plans to get a mastectomy to rectify that. (He won’t do shirtless photo shoots because since he’s under 18, the fatty tissue on his chest would qualify the photos as child pornography.)

But the model isn’t letting fear stop him from using his experiences to reach out to other transgender teenagers over social media. A few months ago, McArthur posted an Instagram photo that showed him crossing his arms over his chest after his first testosterone shot, accompanied by an explanation about overcoming his insecurities about his body.

“I like sharing bits of my life because I think if people can feel closer to me, they can feel a little bit safer about being themselves or a little more confident about being who they are,” McArthur said. “I want to get people to identify with me and see me as a regular person who’s dealing with these issues, because while I’m modeling, I still deal with the same issues that all trans people deal with.”

One of McArthur’s family friends, Marcia Rothschild, said she pegged McArthur as a supermodel when he was just 5. She’s proud of the role model he’s become after going through this journey with him.

“My sadness is not for him as a role model, but for the kids who reach out to him. These don’t have a support system,” she said. “They’re getting kicked out of their houses. They are begging for help.”

McArthur agreed, his voice rising passionately when asked about other transgender teens who look up to him.

“I don’t think it’s fair that kids who are like me, kids who are in the LGBTQ community, kids who are different, have to hide,” he said. “It’s not fair that we have to feel so unsafe in this world. Kids are supposed to be protected by older generations.”

McArthur urges younger generations to speak out for themselves.

“When it comes to your identity, you know when you know. I would not have gone through what I have gone through for something I was not sure about,” he said. “I’m simply telling people that in my opinion, you will only get the highest quality out of life if you are who you are.”