“Forever Young” is yet another “speculative fiction” tale that takes senior citizens for a dainty dip in the Fountain of Youth.

It’s a somber, downbeat drama in which the familiar themes about how old age is “earned” and how some are anxious to “rewrite” their past and others are more than ready to shuffle off this mortal coil are recycled once more.

Those main themes are lightly accesorized in writer-director Henk Pretorious’ narrative. A lost child, a longing for a child never born, old flames and a writer whose audience is dying off are folded into what, at its most basic, is a story of a marriage and the differing expectations each partner brought to it and hopes, in their dotage, to take from it.

Diana Quick, seen in “The Death of Stalin” and in Ridley Scott’s first feature, “The Duelists” way back when, is Robyn White, a 70something novelist who has noticed, via her public readings of her latest book, that her readers aging and dying out.

She’s a bit of a grump, and right-after-a-reading is no time for old flirt Jim (Julien Glover, a memorable James Bond/Indiana Jones nemesis) to shuffle up and demand to know if she’s “writing my book.”

Irritable Robyn isn’t hearing it, even if Jim claims “I’ve discovered the cure for regret!”

Robyn and longtime husband Oscar (“Lord of the Rings” alumnus Bernard Hill) have an old manor house in the country and a routine that depresses her, weekly “Any bets on who’s next?” visits to older friends in the retirement home down the road.

Then Jim shows up again. And this time he looks the way he did when they were all young. Young Jim (Mark Jackson) was “obsessed with age being a curable disease,” and being a Big Brit Pharma chemist, he’d done his share of dabbling.

Whatever he retired with apparently did the trick, and Robyn breaks out her recorder to begin researching that book. “Novis,” he calls his elixir. And when he offers it to Robyn, she’s in a quandary.

Oscar, whom she considers dull and “average,” but who insists to her “that I don’t regret a single day of my life with you,” isn’t interested. He’s got his woodwork diaramas, his occasional “quiz night” at the pub, and Robyn. For him and his little time left, that’s enough.

Researching Jim, she is introduced to the singing, homeless junky daughter (Anna Wolf) born after a one night stand. Hanging with her granny-pal Jane (Stephanie Beacham), Robyn learns she’s headed to Thailand for a cheap facelift.

Two more candidates for the Novis treatment? And what complications might lie with them? Robyn also has to make up her own mind, and it’d be a mighty short movie if she didn’t get into the bath in her ’70s and wake up as her 30ish self (Amy Tyger).

Films like this have to walk a fine line between sentiment and sentimentality. Pretorious avoids that by keeping the temperature entirely too chilly for warmth. He doesn’t give his cast many moments for sentimental reflection or emotional connection with each other, much less the audience.

The stakes feel low, the finale preordained and none of the little sidebars in the “elixir of youth” story serve up anything to make “Forever Young” — a much overused title — engaging or enlightening.

It’s grand seeing Quick, Hill and Glover here, and if there was any heart to the movie it would come from more scenes including all three. “Forever Young” loses its way as it tries to maintain the ties between narcissistic old-and-then-young Robyn and dull but sweetly doddering Oscar, and the extremes she goes to in order to strenghthen that bond.

Whatever Pretorious was going for in the third act, the words “satisfying conclusion” never figured into it, and a modestly interesting not-quite-sci-fi drama wanders into the wilderness in search of its purpose.

Rating: unrated, adult themes

Cast: Diana Quick, Bernard Hill, Amy Tyger, Mark Jackson, Julien Glover, Anna Wolf and Stephanie Beacham.

Credits: Scripted and directed by Henk Pretorious. A Vision Films release.

Running time: 1:40