Helen Mirren and Donald Sutherland take to the road in this soppy bittersweet heart-sinker – depressing in various intentional and unintentional ways. Lovably impulsive oldsters Ella and John infuriate their uptight children (played by Christian McKay and Janel Moloney) by heading off in their cranky old Winnebago for a last road trip in the sunset of their lives, despite their frailties. They are cheerful, gutsy, secretly scared of the future and by imminent revelations about their shared past.

It is an Italian production, directed by Paolo Virzì and co-written by Stephen Amidon, adapting the novel by Michael Zadoorian. (Virzì’s last film was the considerably more astringent, Italian-set Human Capital, an adaptation of Amidon’s novel.)

John is a retired literature professor in the first stages of dementia, given to attempting animated conversations about Ernest Hemingway with baffled waitresses in various diners. For her part, Ella has to take pills for her aches and pains, and the agonies of caring for John are taking their toll. Mirren is caustic and exasperated and has a suth’n accent as Ella, but has to keep softening into a glow of indulgent warmth. Sutherland has the marginally less thankless role as a man entering his second childhood: a snowy-haired babyface of blankness. (I can’t help remembering that his Don’t Look Now co-star Julie Christie also played a person with dementia in the movie Away from Her.)

So how naive are these old people about the ways of the modern world? We get a very coy revelation about their son’s sexual identity, a revelation whose tongue-in-cheek comic flavour feels a bit dated. Would Ella and John really be so naive, or at any rate so reticent? I found it sucrose and glib.

• This article was amended on 20 April 2018 because an earlier version used a term inconsistent with the Guardian’s style guide.