Blake Lively and Harrison Ford play unlikely sweethearts in this sentimental fable

The age difference between Blake Lively and Harrison Ford is 45 years, which might be enough of a yawning gap to give one pause, in the average romantic drama, when they clap eyes on each other and twig they’re long-lost sweethearts. Never fear: The Age of Adaline has an excuse.

Though the title character, as played with a sort of upright, charm-school poise by Lively, is not meant to look a day over 29, she’s actually over 100. A near-fatal accident in the 1930s – snow, dodgy brakes, lightning – produced a medical fluke this gorgeous heroine has revealed to no one whatsoever, except her daughter, in the intervening 80 years. It arrested all outward signs of ageing, making her, to all intents and purposes, immortal.

Immortality is usually creepy on film, even when a story like Dracula invests it with a terrible or forlorn romanticism: no one, save perhaps Bella Swann in Twilight, wants to date the undead. Here it's a conceit for a sentimental fable, like the ageing backwards in The Curious Case of Benjamin Button, or perhaps the Alzheimer’s that arrested true love in The Notebook. Unlike the latter, it’s not a real condition, but we’re asked to accept it as if it were.

The film has a wall of cynicism to get past in the average viewer, who might quite readily play along with the toxic waste accidents or lab mishaps that make a superhero super, but is more likely to scoff, somehow, when an equally unlikely transformation is wrought in a context outside comics. 

If the jeopardy and conflict in those other films is worth the suspension of disbelief, though, we should probably ask ourselves why the crises of the heart in this one shouldn’t be. By taking away the design flaw that makes us human, the film removes from Adaline the possibility of growing old with anyone, and leaves her adrift: come this century, she’s long since given up the trauma of finding and in due course abandoning yet another partner.

That’s until Ellis (Michiel Huisman) shows up, preposterously handsome with his Game of Thrones hair, and also a serial do-gooder who appears to be independently wealthy and did we mention the hair? It would be a match made in heaven, if she would only grow wrinkles and warts like the rest of us. As it stands, she’s hesitant with his come-ons, well aware she could easily break his heart, or at least have some serious explaining to do.

There’s something about this film that heroically resists your mockery, even while semi-intentionally inviting it: the scientific explanations for Adaline’s plight, something to do with “anoxic reflex” meeting 60,000 volts, are so overcranked they’re practically impossible to sit through without smiling. It gets by mostly on shrewd casting. Ellen Burstyn has specialised in playing mothers throughout almost every phase of her 40-year film career. To witness her in the role of someone’s daughter, for once – and especially the daughter of someone a third her age – is the sort of magical role-reversal special effects can’t buy.

Ford and Kathy Baker, meanwhile, play Huisman’s parents, happily married, like the couple in Andrew Haigh’s forthcoming 45 Years, until an unexpected bombshell from his past goes off in their back yard. Ford, usually wheeled on these days to give his films some iconic ballast, hasn’t given such a sincerely emotive performance in years. A young director (Lee Toland Krieger) handles Ford's modest role carefully, as if opening the bonnet on a vintage Model T to hear the engine rumble, then quietly returning it to the garage.

The Age of Adaline is oddly unambitious with 80-odd years of a woman’s past, let alone American history – it feels like a constrained epic, or one with deliberate tunnel vision. But this gives it the virtues of a quaintly disarming fairy tale, refusing any date that isn’t written in the stars.