Speaking candidly to WHO, the star says becoming a celebrity so young has shaped him into who he is today as he prepares to release his first album in almost five years.
“I just always felt a lot older than it was, basically because I left school at 13,” he reasons.
“I moved out when I was 16, 17. I bought my own house and was living in it by myself. I don’t know why it all happened so quick, but it just did. It was a weird thing to navigate.
“It taught me a lot and I was able to travel very young and I’m able to have gained a lot of experience I think a lot of people have around their university years, like 20’s, but I had it when I was like 17,18,19.”
The Gold Coast-raised vocalist – who recently won the first season of The Masked Singer Australia – admits that stardom at a young age came with its fair set of challenges.
“I was kind of an idiot,” he admits. “I was rebelling. I just burnt through everything possible, really quickly. And I’m really glad about that, actually, because I kind of got through it.”
Simpson – who was signed by US label Atlantic Records on his 13th birthday – says he has fellow child star and friend Justin Bieber to thank for getting him through the tougher years.
“I was kind of a couple years behind a couple of the guys and girls that did it first,” he explains.
“So, I got to kind of see what they did wrong. And correct myself as I went along.”
“I almost felt for him sometimes,” Simpson says.
“Being one of the first guys out of the internet generation stars, that was a whole new phenomenon.”
The other integral thing which Simpson credits for helping him veer completely off the rails in his teenage years were his family – parents Brand and Angie, and young siblings Alli and Tom.
“I definitely have gotten slapped upside the head a couple of times,” he admits.
“I’ve never ever been like a douche bag or anything but I definitely had a little phase.
“I was 17 and things were first starting going well, and my mum was like, ‘if you keep acting like this, you’re not coming home for Christmas’. And I was like, ‘well I want to come home for Christmas’.”
The pair collaborated on single “Home To Mama” in 2014 and according to Simpson, his famous pal has been a guiding light for the generation of young stars discovered on YouTube in the 2000s.
Simpson’s rebellion at age 17 coincides with the beginning of his very high-profile relationship with supermodel Gigi Hadid, whom he dated from 2013 to 2015.
Since then, Simpson has been heavily embedded in young Hollywood, and began dating long-time friend Cyrus, 26, in October.
According to the former child star, he and his new girlfriend are both heavily focussed on their health these days after both undertaking their fair share of partying.
“[I had to] party a bunch and get all that out of me and just the minute that I felt like I was done with that, we found each other again,” he says.
When it comes to maintaining his impressive physique, the fit star – who swims competitively – says it’s all about balance.
“I try to eat well five days a week and then the other two I just see whatever,” he says.
“And that seems to be the most long-term sustainable thing. If I can go Monday, Friday and like eat really well yeah. And then Saturdays and Sundays do what, literally eat anything, whatever I want.”
Looking towards 2020, Simpson is mid-way through writing and recording a fourth studio album, his first in five years, and, yes, there’s a good chance there will be a song of two about Cyrus on there.
“I don’t want to say too much about the new album because it’s a surprise,” he says.