So far, the Limerick youngster has taken everything in his stride - recovering from a difficult night against Leinster in early October to make his Heineken Cup debut against Racing Metro 92 and then force his way into the Ireland matchday squad.
Getting capped for your country in the front row at the age of just 23 does not happen often in international rugby.
Indeed, there are similarities between Kilcoyne and the man he replaced during the second half of the South Africa game, Cian Healy. The Dubliner was just 22 when he made his debut against Australia in November 2009.
Healy is now recognised as Ireland's first choice loosehead and a potential Lions tourist next summer. It is a path Kilcoyne would dearly love to take too in the future.
For now, the front rower, whose rugby journey began with the UL Bohemians Under-8s, has his full focus on Fiji tomorrow and his first start in the green jersey.
"For me and the rest of the squad we're treating it as a Test game, so we're putting no focus on the fact that it's an uncapped game - that's irrelevant to us," he said at the team base in Limerick.
"For myself and my family it is a special time, especially playing for an Ireland side at Thomond Park, it's my home ground so I'm relishing the opportunity.
"Hopefully it's a chance to lay down a marker and we'll see what the coaches do from there."
The relish with which Kilcoyne goes about his work in training and matches has left a lasting impression on Ireland forwards coach Gert Smal, who revealed that 'Killer' is a very suitable nickname given the way the young prop applies himself.
Kilcoyne will join forces with Leinster duo Sean Cronin and Mike Ross in the Irish front row tomorrow, determined to maintain the high standards set by scrum coach Greg Feek.
"'Feeky' has done a lot of work and put in a lot of time this week with the new set-ups with myself, Sean and Mike working together and the lads, Cian (Healy) and them coming off the bench.
"It's just a different front row and it's takes a bit of time to get used to but we seem to be clicking quite well."
Kilcoyne knows Ireland will be expected to exert some dominance in the scrum against a nation not known for their ability in the set piece, while also enhancing a lineout that struggled at times against the Springboks.
"Gert and Deccie (Kidney) have put a lot of time into our set piece - our lineout, our maul and our scrum - so that will be a big area of focus. This week we'll really look to that to try and exert a bit of pressure on them.
"The game-plan is to be dominant in the scrum. We don't want to mess around with the scrum and keep the ball in there. We use it as a platform to get the game plan going, so there will be nothing different from that point of view."
Kilcoyne could be excused for pinching himself given his rapid progress through the ranks of club and provincial rugby to the Test arena.
It is interesting to note that the majority of the Ireland XV have played Ulster Bank League rugby in the last season or two, with Kilcoyne and his Munster colleagues Denis Hurley and Conor Murray among that number.
A Division 1B winner with UL Bohemians last season, Kilcoyne also became a British & Irish Cup champion with Munster 'A' and is clearly revelling in being part of the current Ireland set-up.
"I'm loving it up here so I'm going to try and stay here. There are differences in game-plan and structures but rugby's a simple enough game," he admitted.
"There are a lot of Munster players up here. I'm rooming with Donnacha Ryan who I'd be very friendly with back home, so there's not a huge amount of change up here for me anyway."