Hitman thrillers long ago ran out of anything new to do with the genre, lapsing into glib sometime after “La Femme Nikita” back in the ’90s. Nowadays, “glib” isn’t enough. If you’re not aiming for “flippant” like 1974’s “Thunderbolt and Lightfoot,” why bother?

That’s the benchmark film of the “hitman and protege” subgenre, which is where “Old Guy” tries to find a home.

It’s a hired-assassin and his protege thriller from B-movies-made-with-blockbuster-budgets specialist Simon West (“Con Air,” “The Mechanic”), whose lean decades have include “Wild Card,” “Stratton”and “Skyfire.”

As Christoph Waltz has the title role and Lucy Liu’s in it, and it’s set (mostly) in Ireland, it can’t be all bad, right? “Not terrible” about covers it. “Kind of sloppy” is a given.

Waltz is an aged Polish emigre named Dolinski who has finally recovered from the joint-fusion surgery that “cured” his inability to pull the trigger with any confidence. But his boss in “London” (Ann Akinjirin) is all about “a youth movement, across the board.”

Enter young American Wihlborg (Cooper Hoffman). He’s a “prodigy” in this profession, a gauche, tactless teetolater who dresses loudly and is known for killing a few “innocent bystanders” every time he pulls the trigger.

The “Old Guy” with 30 years experience, someone with polish and cunning, even if he’s not as on his game as he once was, is ordered to train his replacement.

“Mr. Millenial? Gen Z? Who can tell the difference?” He has “a lot to learn” from the disco-dancing alcoholic whom the kid assumes can’t miss his “morning nap.”

A twist — the “Old Guy” really has lost his fastball, at least as far as the first act is concerned. But all sorts of scripted shortcomings, cute touches and foreshadowing are tossed away early on, blandly setting us up for a “suicide mission” and its consequences finale.

It’s fun seeing Waltz lose himself on the dance floor as a conflicted character who is often blitzed to his gills. He disabuses the booze, drugs and carbs-avoiding youngster of any delusions Wilhborg has about their “craft.”

“We’re no artists. We’re sanitation workers, taking out the trash.“

But Dolinski has his own delusions, about “never killing anyone who didn’t have it coming.” As “London” is all about taking over “Belfast,” that ethos is about to get tested.

Waltz is kind of fun in the part, as he inevitably is. He tries to give the guy a little humanity, which registers in a sort of ironic way. Liu plays his old friend from a London karaoke bar, and has just a couple of scenes to make a (humorless) impression.

Young Hoffman? He’s a bit lacking in the charisma/screen magnetism thing. The character is blandly written, and the son of Philip Seymour Hoffman can’t find anything colorful — other than wardrobe — to make this guy remotely interesting.

Our screenwriter has only the most facile grasp of the current “generation gap” and those Hoffman’s Wihlborg is supposed to represent, and the writing repeatedly gives this away.

As the film punches through decent stalking session and a couple of good shoot-outs, we’re grateful for the Irish locations if not the mostly colorless villains.

Waltz usually compensates for that, but his burden is too heavy here, and the screenplay and supporting cast offer too little help.

Rating: R, graphic violence, drug abuse, sexual situations, profanity

Cast: Christoph Waltz, Cooper Hoffman, Ann Akinjirin, Tony Hurst, Rory Mullen and Lucy Liu

Credits: Directed by Simon West, scripted by Greg Johnson. An Avenue release.

Running time: 1:33