There is that surname for a start (although his dad is Australian, there are Scots roots further back). Add to that his starring roles in the Proclaimers musical Sunshine On Leith, the north east-set fishing drama For Those In Peril, and his latest film, How I Live Now, directed by Kevin Macdonald, the Glasgow-born, Oscar-winning filmmaker.
Would adoption be an option then? "Please, if I could be part of that clan it would be most appreciated," says the 21-year-old, laughing.
How I Live Now, adapted from the best-selling novel by Meg Rosoff, follows the finest traditions of young adult fiction in examining big issues - in this case war, peace and love - with the clear-eyed gaze of the young.
MacKay plays Eddie, one of three youngsters living an idyllic if shambolic life in the country while their mother, a diplomat, is off trying to save the world. When their cousin Daisy (Saoirse Ronan), a highly strung New Yorker, comes to stay it looks like her phobia about germs will be the summer's biggest headache. How wrong they turn out to be.
For the first time, MacKay, whose screen career began when he was nine with Peter Pan, was the old bones in the cast. "I've always been the youngest," he says. He made friends quickly, though, and there was always Raj to hang out with, Raj being a hawk his character rescues. After some coaching with a trainer, bird and self-dubbed "city boy by circumstance" got along famously.
"The first time I handled her she was really insecure because she felt I was nervous. But as soon as you are both comfortable with each other she relaxed a lot. It's funny, I would have thought you would give them their space but they actually feel much more comfortable and secure the closer they are into the body and the less they can see. I'd carry her around the set as much as I was allowed to." And there were no nips. "She was all good."
Though the film is more about love than politics, MacKay says the subject matter of How I Live Now did make him think more closely about the "faceless nature" of war today.
"It does make you aware of it, how quickly things can happen, and how lucky we are. You would not get out of bed in the morning if you were constantly worrying about the possibility of something happening to you on your way to work. But it is still something to pay attention to, I think."
MacKay's younger sister was a fan of the book, and he read it as part of the auditioning process. For MacKay, the biggest attraction was the chance to work with Macdonald, the director of Touching The Void, The Last King Of Scotland and State Of Play.
"I was really excited and a bit nervous to work with him because I knew his other work and what a great director he is. I still could not really work out on set what it was that makes him so good, but I think it is the kind of vibe he creates."
Macdonald had firm ideas about Eddie, and the actor who would play him. "I didn't want a smooth-skinned Twilight pretty boy, I wanted somebody who felt like they were a country boy, and who had the awkwardness and mystical quality that Eddie is meant to have."
Macdonald's documentary background particularly paid off in the scenes where the four are left to fend for themselves, says MacKay. With Macdonald hanging back, the youngsters were able to forget everyone else was there and act like a normal family.
Next month, MacKay will be seen in For Those In Peril, a drama about a fishing boat tragedy that had its UK premiere at the Edinburgh International Film Festival in June. Filmed in north east Scotland, the subject was again harrowing, but as with How I Live Now, the director, Paul Wright, and cast, including Kate Dickie playing MacKay's mum, made all the difference.
"I just had the best time doing it. Everyone went to some pretty dark places at certain times but it was one of the most joyous experiences I have ever had on a set because we felt so involved. Paul is very involving and I got to spend so much time with him. To feel part of something as much as he made you feel part of it, and really encourage your opinion, was exciting."
In For Those In Peril and Sunshine On Leith, out this week, MacKay had to learn a north east accent and an Edinburgh one. A dialect coach helped, as did MacKay's natural ear for speech patterns.
"I seem to have a bit of a knack for accents, I can pick them up quick enough. I had a broad idea of the Scots accent; it just so happened my idea of it was mainly East Coast but with a bit of Glasgow in there. It was about honing it in to a more specific spot."
When he auditioned for Sunshine On Leith, the tale of two squaddies returning home to Edinburgh set to the songs of The Proclaimers, he sang the film's title song, plus Misty Blue and Make My Heart Fly. As with Raj the hawk in How I Live Now, MacKay, who played in a band after he left school, wasn't alone. "I was allowed to take my guitar."
Since Peter Pan in 2003, MacKay has worked consistently, following television parts (Rose And Maloney, Tsunami: The Aftermath) with films.
He would have liked to have gone to drama school, and auditioned for two in London. In the drama school equivalent of the publishing houses that turned down JK Rowling, he did not get in. That made his decision for him. Reasoning that he would carry on working and perhaps try again later, he has barely been out of a job since. With four films out this year, one next, and another project under way, it was a good call.
He would still like to train at some point, but like any young actor he is reluctant to step off the merry-go-round lest he is unable to get back on. "I would be a bit nervous to stop for three years at the moment." Besides that, he says, you learn so much on the job.
Having spent time in Scotland for the Sunshine On Leith premiere, he is back in England and back at work on a new film, a drama set in the 1980s. Home is with his parents in London. "Aye, for the time being," he says. MacKay has left Scotland for now, but Scotland has clearly not left him.
How I Live Now opens tomorrow. For Those In Peril opens in Scotland on November 8.