And with hookers Stephen Moore and Tatafu Polota-Nau now nursing knee injuries, Charles is set to be thrust into a starting role for the Wallabies' Bledisloe Cup opener against the All Blacks in Sydney on August 16.
At 25, Charles is living his dream. But it hasn't always been smooth sailing - far from it in fact.
When he was 3 months old, Charles was diagnosed with cystic fibrosis (CF) - a genetic condition that has no known cure.
His parents, Heike and David, were told the grim news that Charles would be lucky to make it to his 10th birthday.
"Our world fell apart," Heike says. "We now know what shock is all about."
David was equally numb.
"We were a wreck," he says.
"The life expectancy, the stories we were told, the other kids that we saw ... it was devastating."
CF affects a number of organs in the body, especially the lungs and pancreas, by clogging them with thick, sticky mucus.
Repeated infections and blockages can cause irreversible lung damage and even death.
To stay on top of the condition, Charles takes up to 16 vitamins and 12 medications every day.
But for a CF sufferer to live a normal life, they need to ensure their lungs remain active.
Charles has his parents to thank for helping him build a strong set of lungs that have carried him all the way to the top level of rugby.
"Until he was old enough to play sport we used to have games like trampolining and blowing up balloons," Heike says.
"And since then he's played every single sport you can think of - rugby, touch football, swimming, basketball, AFL, indoor soccer, water polo, athletics, baseball.
"The only thing we talked him out of was cricket, because it wasn't as active."
Charles is the only known professional athlete with CF playing a contact sport.
"It's something I'm pretty proud of, and I hope I can use that to inspire others with CF to push for higher goals in life," Charles says.
In 2010, he became an ambassador for Cystic Fibrosis Australia.
It was a role Charles was initially hesitant to take for fear people would judge him on the condition rather than his rugby skills.
"I want people to view me as a rugby player rather than a person that carries the condition," Charles says.
"It's very important to me. I don't want people to sympathise with me one bit.
"I want to be commended on a good performance, and on the other side criticised if I haven't put in a good performance.
"Everyone has their own barriers in life and this is mine."
Charles has a history of making the most of any opportunity that comes his way.
In 2010, Charles was signed by the Western Force on a short-term deal after Ryan Tyrrell suffered a season-ending neck injury.
It was a make-or-break chance for Charles, and his length-of-the-field sprint in a famous 24-16 win over the Crusaders helped seal a permanent deal for the nippy front rower.
"He came over from the Brumbies academy, and he only had three or four games to prove himself and possibly get a contract," Charles senior says.
"In my opinion, that run against the Crusaders enabled him to achieve that.
"He played centre until he was about 11 or 12, so he's always had that burst of speed."
Charles seemed destined to land a Wallabies gig after establishing himself as the Force's first-choice hooker in 2011 and 2012.
But when he busted his knee early last year, that goal seemed a long way away. Not even in Charles' wildest dreams could he imagine a Wallabies debut in 2014.
But after producing a string of impressive performances in his comeback year for the Force this season, Charles was rewarded with a Wallabies debut against France.
Wallabies coach Ewen McKenzie is already a big fan of Charles, labelling the hooker as a medical marvel who defies science and logic to achieve his goals. But for David and Heike, their son's achievements come as no surprise.
After all, they've seen first-hand the hard work Charles has appliedto stay healthy and fulfil his dreams.
And as for the nickname Cheezy?
"His brother has always been called Cheezy," Heike says with a laugh.
"For a while they were at the same school, so they called Nathan Mini-Cheese. But then Mini-Cheese got bigger than Big-Cheese!"
Charles' reputation is also getting bigger. More and more people are becoming inspired by his story.
Now the time has come for the next step in his journey - a starting role against the All Blacks.
Who knows, maybe even Kiwis will be wishing him luck?
- AAP
