This is basically a geriatric version of “The Hangover”—four seventy-somethings go off to Vegas for a bachelor party—but since the target audience is clearly closer in age to the lead actors than to the moviegoers who made Todd Phillips’ slob comedy such a smash, the comedic tone of Jon Turteltaub’s movie is understandably gentler—naughty rather than nasty. “Last Vegas” is just an attempt to dust off the “Grumpy Old Men” playbook for the next generation of older stars, and it hardly breaks any new ground. But though thoroughly predictable, no more than mildly amusing, and utterly maudlin when it veers into sentimental mode, it’s a harmless enough vehicle for some old-timers to strut their stuff, a cinematic soft-shoe routine that’s definitely worn but tolerable.

The sparkplug of the plot involves the decision of wheeler-dealer and confirmed bachelor Billy (Michael Douglas) to pop the question to his thirty-something girlfriend (Bre Blair) while delivering a eulogy for a friend (and obviously feeling his own mortality). Quickly planning nuptials at a Vegas chapel, he phones two of his closest buddies—Archie (Morgan Freeman), who’s being smothered with concern by his son (Michael Ealy) after suffering a mild stroke, and Sam (Kevin Kline), who’s living in Florida with his understanding wife (Joanna Gleason)—to invite them to the ceremony. He tasks them to persuade the fourth member of their childhood Brooklyn posse of the fifties, Paddy (Robert De Niro), to come as well. The problem isn’t merely that Paddy has turned into a recluse following the death of his wife, but that he’s furious with Billy over his failure to attend her funeral. Of course, Paddy eventually tags along anyway, though his mood is surly, especially after he finds out the reason for the trip.

A lot of what ensues is by-the-numbers. The fellows bicker and party in approximately equal measure. They ogle young girls—especially Sam, whose wife has given him permission to cut loose. They gamble—especially Archie, whose skill at blackjack brings them special treatment at a casino, including a lavish penthouse suite and a personal concierge named Lonnie (Romany Malco), who’s initially disappointed that they’re not the famous rapper he’d expected to have as his guest but eventually warms to them. There’s also a curious plot turn involving them being passed off a mob guys in order to put an arrogant young twit (Joey Ferrara) in his place.

But the main thread involves the quartet getting to know Diana (Mary Steenburgen), a singer in a tiny casino lounge whom both Billy and Paddy find attractive. She’s a wisecracking but emotionally vibrant person whose presence brings up a great deal of past history the two men share which, while initially widening the breach between them, is ultimately the cause of their reconciliation—and of Billy’s finally realizing what he really needs.

The humor in “Last Vegas” is mostly very mild and sitcomish, banking on how cute these four geezers are as they have fun amidst the glitz of the city (which, of course, is periodically spotlighted in montages that are a recurrent element of David Henning’s standard-issue cinematography). And viewers can rest assured that all the plot threads work out for the best. That’s true even of the thread that finds Sam searching for somebody to share his condom with, which leads him first to hit on a lady at a bar who turns out to be a guy in drag (Roger Bart)—a interlude that’s the basis for a little lesson in friendly acceptance of people different from you—and then nearly to score with a young bridesmaid—an episode that turns into a lesson about marital fidelity.

The stars seem to be having a good time despite the feebleness of the material. Billy certainly doesn’t strain Douglas’ acting muscles the way Liberace did, but he’s agreeable enough, while De Niro tones down the gruffness of his earlier comic turns in “Meet the Fockers” and “Analyze This” (not to mention “The Family”) a bit this time around, to good effect. Freeman pretty much coasts on his affability, and though a saccharine scene with Ealy toward the close could have well been excised (like most of the obligatory sentimental moments scattered toward the finale), another that gives him a chance to show off on the dance floor is pleasant. Kline outstrips the others, however, often enlivening scenes that have little or no potential through sheer force of will, and Steenburgen is her usual charming self, like Kline transcending what she’s given to work with.

Nobody would acclaim “Last Vegas” as any kind of comic classic. But as a vehicle for these four familiar faces, it’s a genial enough bit of old-timer fluff, especially with Steenburgen tagging along for the ride.