Fast forward four years and, now 22, the full-back/winger has become one of the most exciting talents in the country.
He has 11 full caps and looks likely to head to Japan with Gregor Townsend’s men for the World Cup later this year.
A bright individual, Kinghorn never appears to get too far ahead of himself and, as he continues his rehabilitation from an ankle injury in time to start Scotland’s summer training camp in mid-June, he remains level headed.
“I had a couple of injuries when I was at school, but this has been my first real long-term one as a professional in four years with Edinburgh, so I guess I have been pretty lucky. It is just part of the game,” he said as he took time out from his recovery which has been going on since mid-March.
“I was over the moon to be named in the training squad for the World Cup and in recent weeks my sole aim has been making sure I am back fit for mid-June.”
While he was out during April and earlier this month, winger Darcy Graham moved into his No 15 jersey for Edinburgh and acquitted himself well.
“I don’t think I will play full-back again,” joked Kinghorn.
“Seriously though, I have known Darcy since we came up through the age-grade levels and it has been great to see him getting his chance with Edinburgh and Scotland and he has grabbed it.
“Obviously he played a lot of sevens in 2017-18 and that really helped him in an attacking sense.
“When he gets the ball in his hands the crowd light up and the defenders that he is heading towards are on alert because you never know quite what he is going to bring with his quick feet.
“He can change direction very quickly and brings a lot to the table and I look forward to playing with him more in the future.”
Meanwhile, Kinghorn has paid tribute to two “role models” who have helped him get to where he is in recent years.
They are retiring Edinburgh and Scotland hooker Ross Ford and Edinburgh and Fiji No 8 Viliame “Bill” Mata who is set to play against England this coming weekend for the Barbarians at Twickenham.
“I sat quite near him in the changing rooms so it will be strange next season when he is not there,” he said of Ford.
“He epitomises hard work, he just always came into training and did what was needed with no fuss.
“He will be missed around the place and I wish him well. He has been awesome, he is some man, he is a complete legend.
“Bill can create something out of nothing, he never complains about putting in the hard yards at training and that is testament to his character.
“He is very quiet, very humble, but he is an awesome, awesome player.”
Edinburgh’s 2018-19 season tailed off as they missed out on a Guinness Pro14 play-off place and a Heineken European Champions Cup spot for next term.
Kinghorn stated: “I think overall our season was pretty good and we are always improving as a squad. We just had a couple of bad results towards the end of the campaign that let us down.
“This is the strongest squad I have been involved in during my time at the club. We have obviously lost some good players, but we are definitely heading in the right direction.There are quite a lot of little things that we have to fix in our game in terms of attack and defence, but we can do that and next season will be better.”
Kinghorn has been getting through the long hours of rehab in the BT Murrayfield gym with his Edinburgh team-mate Lewis Carmichael, the 24-year-old second-row/back-row who is recovering from torn ACL.
And you get the feeling they should both stick to rugby rather than beard growing.
“Me and Lewis had a bet to see who could grow our beards the longest, but we called a truce because we both looked a bit disgusting; it wasn’t the best,” baby-faced Kinghorn admitted.