Richard Linklater's latest film was shot over 12 years as a child grows up and his parents grow old. It's the most brilliant example in a series of films which challenge the audience's relationship with actors, and with what makes a narrative

On a bright, cold morning at the Sundance film festival, the delegates gathered to see a film that put the world in a bottle, folding a 12-year span into 164 minutes. Richard Linklater's Boyhood chases a Texas kid into manhood and spotlights a changing America at the edge of the canvas. On screen, in leaps and bounds, little Mason grows up while his parents grow old. There are no morals, no life lessons, just the heart-tugging, heartbreaking gallop of the years. Watching the drama, transfixed in the dark, I recalled the old Dylan Thomas poem about the the apple towns and the foxes on the hill. "Time held me green and dying," it goes. "Though I sang in my chains like the sea."

Is it presumptuous to claim Boyhood as my film of the year? In the first place, 2014 is barely six months old. Second, I'm not quite sure to which year it belongs. Do we date Linklater's film from 2001, when he first conceived the project, or does it have a toehold in all the intervening years, when the picture was assembled, largely under the radar? I'm not sure. Boyhood is quietly confounding and quite possibly unique. "It almost isn't even like a film at all," Linklater tells me. "It's somewhere between summer camp and an art project. It's like a time sculpture."

Film is a narrative and narrative means time. The ticking clock is cinema's building block (if you're feeling generous) or its stumbling block (if you're not). Industrious directors might break up the flow with flashbacks and dissolves and those lookalike actors. But this is usually just an array of tricks and misdirection; crass cosmetic surgery, designed to outwit the ageing process. More often than not, it is the films that look foolish.

A more grownup Mason.

"The length of a film should be directly related to the endurance of the human bladder," said Alfred Hitchcock, a man with a keen understanding of both cinema physics and the excretory system. Yet what of the time inside the actual film? Hitchcock himself experimented with real-time drama on his 1948 thriller Rope, which affected to frame the entire story (murder, coverup, investigation and discovery) in one single, continuous take. Still, it's no accident that most conventional dramas play out over a period of a few weeks or months. That, after all, is the average length of a movie's production.

Stretch the time frame more than that and the illusion breaks; the elastic snaps. The lookalikes, put bluntly, do not look alike, and the latex ageing makeup is invariably a joke. Yes, Robert De Niro did a superb job of bulking up to play the debauched, middle-aged Jake LaMotta in Raging Bull. But what of Leonardo DiCaprio, piled under plastic at the end of J Edgar? Hapless James Dean at the finale of Giant? Russell Crowe in A Beautiful Mind? Any number of others? Even Citizen Kane, traditionally touted as the most cinematic film in cinematic history, pitches towards vaudeville the moment 25-year-old Orson Welles staggers on screen with his crinkly bald wig and snowy moustache.

Is it ever possible to swerve past these stumbling blocks? Steven Soderbergh found a novel solution in his 1999 film The Limey – lifting portions from 1967's Poor Cow and using them as flashbacks, to show us Terence Stamp in his youth. But that remains an anomaly; it's a copyright minefield. Films can be magical, they can travel through time. But they must do so like we all do, one step at a time and matching their rhythms to the ticking of the clock.

Mason Jr and Sr (Ethan Hawke).

"There's always a life metaphor," says Linklater, who convinced IFC Films to let him shoot Boyhood in brief four-day bursts between 2002 and 2013, with the release date flung out to the horizon. "How do we plan for our own futures? You do your best but you live in the present. So it was the same thing with the production. You know you're collaborating with an unknown, random future element. All you can do is keep marching towards it, and adjust yourself as the reality shifts."

Boyhood, then, in effect wrote itself as it went along. It made its path by walking it. At times, Linklater was content to take his lead from the true-life experiences of his lead actor Ellar Coltrane, who grew up in parallel with the character he played. At others, he allowed contemporary events (the war on terror; the election of Obama) to leave their thumbprints on the tale. If one of his actors had died, he would have had to incorporate that too. "But you've got to play the statistics," he says. "There were really five main people [in this movie]: the four family members and myself. The odds were that we would all be here 12 years later." Boyhood, for all its domestic ructions and bittersweet edge, was a fundamentally optimistic venture.

Is Linklater's process unprecedented? Possibly not; it has ancestors and cousins. Here in the UK, director Michael Winterbottom elected to shoot his prison drama Everyday over a five-year period, embedding a real-time ageing process into the fabric of his film. On the small screen, Michael Apted's Up documentary series remains a going concern, revisiting its subjects at regular intervals. I'm looking forward to seeing how Apted's offspring (bullish Tony; fragile Neil) are faring at the age of 63, when we are next due to meet them.

Until then, though, I'm quite happy with Linklater's film, which is funny and sad, mundane and outlandish; a movie that looks just a little like life. Boyhood invites us to look afresh at ourselves as children and ourselves as parents, and a world that is changing, incrementally, beneath our very noses. And if that is emotional for the viewer, just imagine what it must feel like for youthful Coltrane, who signed on for the role at the age of just six and has only recently viewed the fruits of his labours.

The experience, he admits, was deeply bizarre. "To see things that I don't entirely remember doing. To see this little person that I don't really remember being. But it's incredible," he adds. "It's catalysed a lot of things. I think I've grown up since watching it."

• Boyhood is released in the UK on 11 July.