Following a successful stint on Celebrity Big Brother this year, the 34-year-old has released a best-selling book and is currently the face of a new range for menswear store Burton.
Speaking to the Daily Star, Calum admitted: "It's been an ongoing process. In my younger years I made silly mistakes that I hold my hands up to.
"I didn't know what path I wanted to take. But now I'm making an effort to be more private, working out and being healthier, so I don't make any stupid public mistakes that I made before. I've grown up and become a man now."
Despite this, Calum insists he's not passed it just yet. He continued: "I am fun.
"I might eat organic and drink green juice, but when it comes down to it, I still enjoy a night out."
But, after struggling with alcohol in the past, Calum is careful not to split back into bad habits.
He continued: "I have to keep those nights few and far between, because I know how easy it is to get sucked into that world.
"I still have that [bad boy] in me. I can still go on a night out and I know how to party."
Calum recently split from girlfriend Ianthe Rose Cochrane-Stack, and he confessed he's not interested in girls throwing themselves at him.
He added: "I'd never say I have my pick of women. But yeah, it was fun and games in my younger years."