When it comes to age-gap films starring Nicole Kidman, Jonathan Glazer’s Birth is surely impossible to follow. But newcomer screenwriter Carrie Solomon and director Richard LaGravenese are trying it with this romcom for Netflix which, despite a very cute high concept, resolves the unresolved sexual tension too early and jettisons the irony and comedy well before the end of the first act, leaving us with something a bit solemn.

The film in fact reunites Kidman with Zac Efron; they starred together in The Paperboy in 2013. Efron plays Chris Cole, a shallow and vain young movie star in LA who mistreats his much put-upon assistant Zara, kookily played by Joey King. With much pouting and eye-rolling she has to cater to his every whim and it is especially her job to organise the purchase of the special “breakup” diamond earrings that Chris always gives to young women he’s going to dump.

Then Chris meets Zara’s incredibly hot widowed mother Brooke Harwood (Kidman), a celebrated writer whose early inspiration is Joan Didion; her sensitivity unlocks Chris’s hidden niceness and vulnerability and they have rock’n’roll age-gap sex to the horror and disgust of Zara, who still has to pick up Chris’s dry cleaning.

The initial setup is great, the Ephronesque excitable phone conversation montage is tolerable, but the cliched breakup and makeup plot transition clanks. When Chris has to magically stop being a hilarious airhead and start being Mr Perfect, things become pretty insufferable. And there is an extraordinary moment when Chris gives Brooke her Christmas present: a weirdly cheap looking book with gold-embossed lettering called The Brooke Harwood Anthology: “It’s got all your essays from the New Yorker and Vogue and all your stories in one place! You like it?” – “I love it!” Didion would have told him to stick his homemade book where there is an absence of sunshine.

• A Family Affair is on Netflix from 28 June.