For a vivid lesson in the toll that time exacts from us all, consider two images of Peter O’Toole. First, imagine his debut performance as the title character of 1962’s Lawrence of Arabia, striding across the roof of a recently sabotaged train. Sun-kissed, white-garbed and vigorous, he both conveys T.E. Lawrence as a messianic poet/warrior and anticipates his future career portraying larger-than-life personalities.

Then, look at him in his latest film, the melancholy comedy Venus. At 74 years old, O’Toole literally resembles a ghost of his former self. His eyes are sunken, his pale skin is nearly translucent, and his handsome features are now on the verge of sinking into his ascot. Time has turned the matinee idol into a will o’ the wisp.

It might seem harsh to spell things out so bluntly, but growing old is a harsh thing, and Venus doesn’t stint from facing mortality. Plus, it’s hard to imagine this film directed by Roger Michell (Notting Hill, Enduring Love) being nearly as effective without an actor of O’Toole’s renown in the central role. His presence, and our memories of his younger self, elevates a film that otherwise would be insubstantial despite its cleverness and sensitivity.

O’Toole’s Maurice Russell and his obstreperous friend and colleague, Ian (Leslie Phillips), are both veteran actors who make a hilarious duo with spot-on comic timing. In the early scenes, Ian none-too-subtly brags that his grand niece Jessie is going to move in with him, as a kind of comely nursemaid and personal shopper. When Maurice next visits, Ian appears in a state of horror, describing Jessie in monstrous terms. Jessie (Jodie Whittaker) turns out to be a pretty but ordinary young woman—sullen, slumping and unimpressed by the elderly.

Maurice, characteristically and quixotically, becomes smitten with her despite her uncouth habits. They don’t speak the same language—almost literally, given Maurice’s thespian elocution and Jessie’s thick slang. Maurice nicknames her “Venus” after the goddess of love, and probably thinks of himself as Professor Henry Higgins in My Fair Lady, bestowing sophistication on a young woman. Outsiders such as Ian probably consider him more like Humbert Humbert leching after Lolita’s underage girl. Jessie probably thinks of him as something between a sugar daddy and part of the furniture.

Maurice’s attentions fall somewhere between lust and longing, since prostrate trouble has rendered him impotent, although Jessie gradually permits some chaste touching. Hanif Kureishi, writer of Sammy and Rosie Get Laid (1987), authored Venus’ script and makes an effort to establish an ethos of transcendent pleasure. Maurice tells Jessie that most men will never see anything as beautiful as a woman’s body, while for a woman, the most beautiful sight is that of her first child. But does the observation convey wisdom, or just smooth patter to talk a woman out of her clothes.

Being whittled down to life-size deepens O’Toole’s craft in an unexpectedly new way. With his height, aristocratic bearing and ringing voice, he frequently played madmen, artists and kings. Maurice may be one of the most “ordinary” men he’s ever played, and though he can recite “Shall I compare thee to a summer’s day?” with aching beauty, he fleshes out Maurice’s more naturalistic qualities with surprising grace and realism.

And though O’Toole himself may be physically frail, the worse for alcohol and illness much of his life, he doesn’t shy away from Venus’ physical comedy. He gets Jessie a job as a nude model for an art class, but she refuses to allow him to watch, and when he tries to peek over the studio transom, he comes pratfalling into the room, knocking over easels like dominos.

Venus nevertheless feels like a small story with an inconsistent tone. Some of the film’s quirky moments have an artificial vibe, such as Maurice and Ian’s impromptu waltz in a chapel. There’s a particularly unsubtle moment when Maurice and Jessie ride a limo to a film location. The camera cuts between Jessie’s top half sticking out the sunroof, enjoying the luxe life like a prom date, and Maurice sitting beside her lower half, ogling her mini-skirted legs. At such moments, Venus evokes Steve Martin’s quip: “I believe that you should place a woman on a pedestal, just high enough so you can look up her dress.”

VENUS ( * * * )

Directed by Roger Michell. • Starring Peter O’Toole and Jodie Whittaker. • R, 95 min. • At the Osio Cinemas.