It was all brought home in his first training session: "We were doing the final drill, line up and tackle the first bag, then tackle second back, and so on as you and work your way along," he recalled. "We did it in age order - oldest to youngest - so I placed myself in the middle of the line. Then I realised everybody was looking at me.
"I remember from the old Edinburgh days when most of the team was late 20s, early 30s but these days are gone. Dicko [Alasdair Dickinson, the prop] was the oldest at 30; at 26 I was third in the line - I couldn't believe it. There were a few guys missing but you also have guys of 19 or 20 who are pushing for first-team places, which can only be encouraging. It is great for the team."
He accepts, however, that the youth around him is not an excuse for another season of failure. After importing a load of talent and giving both the incomers and the home-grown players the preseason training he believes they need, Alan Solomons, the head coach, has no excuses left if the team does not perform.
So while McKenzie is full of praise for the way Solomons has insulated the players from that pressure, they all know it is there and firmly believe that after five seasons of relative obscurity, they are ready to turn the corner with results that matter.
"There is pressure on us," McKenzie said. "We need to perform and achieve as high a position in the league as possible; do well in all competitions. There is a great buzz around the club. There has been a lot of transition in the last couple of years but if you look at it, it is an extremely young squad. There are guys who are experienced in terms of games who are only 22 or 23 years old.
"Top six [in the league] is a minimum, we want to be playing in the top competition in Europe. We want to prove we are not a diddy team. When a team comes to us we want them to know they have been in a match."
He may find himself among the senior brigade but it is also a chance for him to reboot a career that has pretty much stalled since he went to play south of the Border. Back home, where he is happy, comfortable and in demand, he is even able to shrug off the exhaustion of a preseason that has been every bit as tough and brutal as Solomons promised, and look forward with optimism.