YOU don’t have to be over 40 to enjoy “Still Crazy,” but … well, actually you do.

This flaccid but pleasantly tolerable British comedy about the regrouping of a fictional ’70s rock band is meant to rouse aging baby boomers who fear they’re uncool and too old to rock ‘n’ roll – and fear impotence.

It’s a ripe subject for satire, and “Still Crazy” could have been a rollicking, uproarious send-up of boomer vanity and rock cliches. But after a promising beginning, director Brian Gibson gives in to a therapeutic approach that flatters its haggard audience with an unabashedly sentimental pep rally – the cinematic equivalent of St. Joseph’s Baby Viagra.

If you find charming and inspirational the idea that a twentysomething groupie is obsessed with giving the full Monica to a blubbery old hairball of a drummer, “Still Crazy” will be heartening.

The group is called Strange Fruit, a pompous, stadium-rock “hair band” in the mold of Aero-smith and Led Zeppelin. The Fruit broke up acrimoniously at a 1977 English rock festival. As the Fruit’s roadie, Hughie (Billy Connolly), observes in voiceover, “I think God got sick of all that ’70s excess. That’s why he invented the Sex Pistols.”

As the action begins, Fruit keyboardist Tony Costello (the ever-droopy Stephen Rea) handles the condom-machine concession in the Spanish resort town of Ibiza, where he has a chance encounter with the son of the festival’s promoter.

The kid is planning an anniversary fest reunion, and asks Tony to re-form the group for the gig.

Tony hooks up with Karen (Juliet Aubrey), the band’s former personal assistant, and sets out with her to find the surviving Fruits. Les (Jimmy Nail), a bass player-turned-roofer, joins hesitantly, while Beano (Timothy Spall), the doofus drummer, leaps in feet first, desperate to make enough money to pay off the tax man.

The best performance in a well-055 . 0000.00acted movie is Bill Nighy’s turn as Ray – the Robert Plant-like, preserved-in-amber lead singer. Ray lives far beyond his means in a giant mansion with his haughty young Scandi-babian wife, Astrid (Helena Bergstrom), releasing solo albums nobody wants to buy and struggling to stay off the sauce.

Nighy is terrific as a once-Byronic figure who’s as dessicated as beef jerky and utterly terrified of aging.

They undertakes a tour of clubs in Holland, trying to work the kinks out, but their old animosities and chronic insecurities threaten to put the kibosh on what they hope will be a triumphant return.

The cast may be endearing, but the wheezy material is mighty soft in the belly. While not without amusing moments, the screenplay by Ian LaFrenais and Dick Clement takes the sweet old geezers through the expected motions and 055 . 0000.00obvious gags, but there’s not much wit or cleverness here.

It recalls the way Hollywood filed the fangs off the stage version of “Steel Magnolias” to confect a squishy tribute to sisterhood. And if the music were any good, that’d be one thing, but does anybody really long for the resurrection of that Emerson, Lake and Palmer brand of sludge?

In their big comeback number here, Strange Fruit bleats rock-goddishly (with lyric-writing assistance from Foreigner’s Mick Jones) about “the flame [that] still burns/it’s there in my soul.”

Hey, Pops, that’s just gas.

STILL CRAZY Starring Stephen Rea, Billy Connolly. Directed by Brian Gibson. Running time: 95 minutes. Rated: R. At the Lincoln Square and Union Square 14 theaters.

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