Christoph Waltz in Simon West’s Limp Action-Comedy

Memo to Quentin Tarantino: Please go back to making movies again soon, and write another great part for Christoph Waltz, stat!

The urgency is prompted by Old Guy, the mediocre new action-comedy (a genre that really, really needs good execution to work) in which the two-time Oscar winner plays Danny Dolinski, an aging hitman going through, you guessed it, a midlife crisis. Danny is suffering from arthritis and recently had joint fusion surgery, which makes it particularly painful for him to shoot a gun. And his boss (Ann Akinjirin) informs him that, after 30 years of service, his workplace days are numbered and he has to train a much younger protégé.

“We’re going younger across the board,” she informs him, sounding like Elon Musk addressing the newly fired employees of a government agency.

For some reason, filmmakers have long been of the opinion that hired assassins are just like us, worried about such things as getting older and job security. But even when played by an actor as charming and charismatic as Waltz, it’s hard to get worked up over the problems of a killer — even if, as in this case, he’s soothingly sweet to a little girl just before murdering her grandfather.

Of course, Greg Johnson’s screenplay is pitched less for sentiment than humor, which would be fine if it possessed the wit of, say, Grosse Pointe Blank. Here, cleverness is in distressingly short supply, unless you count the younger hitman sarcastically addressing Danny as “Obi-Wan” to be hilarious.

The trainee, addressed only as Wihlborg, is described as a “hitman prodigy” even if he does have the unfortunate habit of accidentally killing innocent bystanders. Derisively labeled “Gen Z” by Danny, he displays various eccentricities, including painted fingernails and a necklace featuring a miniature racecar. He’s played by Cooper Hoffman, whose baby face makes him look even younger than his 21 years. The son of Philip Seymour Hoffman, he already demonstrated his burgeoning talent in the film Licorice Pizza. But he seems woefully miscast here. A bowling prodigy, sure. A math prodigy, absolutely. But a hitman prodigy? Not at all.

The relationship between the two men naturally proves combative, with Danny unwilling to relinquish his status and Wihlborg impatient with his trainer’s refusal to acknowledge his limitations. Danny is the sort of hard-partying, hard-drinking hedonist who wakes up with multiple undressed women in his bed, while Wihlborg refers to his body as a temple and disdains liquor and carbs. The film attempts to derive much humor from their culture clash, with little success.

It’s even less impressive in the action department, despite being directed by Simon West, who has demonstrated his talent in that regard with such bigger-budgeted films as Con Air and Lara Croft: Tomb Raider. There’s plenty of gory violence in Old Guy but little real excitement, and serious pacing issues as well. It’s also hard to get emotionally involved when Danny and Wihlborg overcome their animosities and team up after their employer betrays them.

Lucy Liu is also on hand as Anata, an old friend of Danny’s, although what her character’s purpose is in the story proves hard to discern. She seems to be tagging along with Danny for no good reason, even if she does manage to get him out of a dangerous situation at one point. But a lengthy scene involving Anata’s romantic troubles feels awkwardly shoehorned in, and Liu, despite her impressive skills, feels extraneous to the proceedings.

Old Guy benefits from its extensive use of scenic Northern Ireland locations. But by the time the Austrian-accented Danny goes to visit his elderly mother, who speaks with an Irish brogue, it’s long become clear that credibility was not a major concern.