If you are one of those people who think superannuated rockers from the late 1960s have no business going on tour, you will get a kick out of Neil Young’s new film, CSNY: Déjà Vu.

It is nearly 40 years since the heyday of the folk-rock super-group Crosby, Stills, Nash & Young, and this documentary charts the reunion of the old gang in 2006 for one more road trip.

Musically, as Young admits in a voiceover, the early part of the tour was “a bit rough”.

Then, at the climax of Young’s Rockin’ in the Free World at a show in Toronto, Stephen Stills stumbles and falls over mid-song.

Lying among the speakers at the front of the stage and still trying to play, he can’t get back to his feet and has to wave off a youthful helping hand. The indignity of it all.

All this is just fine with Young. At 62, he is angry and out to make a noise; the uglier it all gets, the better he seems to like it.

The cause of this anger is the war in Iraq. Young was only in his mid-twenties when he wrote Ohio, a protest song prompted by the killing of four students at an anti-Vietnam war protest at Kent State University.

The times and the war may have changed but Young’s simmering discontent over Iraq finally boiled over in early 2006 and he rushed off a new album of protest songs, Living with War.

That was followed by a US tour supported by Crosby, Stills and  Nash — a group of musicians famous for their feuds, break-ups and reformations.

The film of the tour is Young’s attempt to keep fanning the flames, a journey of protest through the American heartland, an act of angry defiance.

Of course, that word “angry” should come with a large asterisk next to it.

A Canadian and a product of the 1960s counterculture, Young doesn’t really do anger that well. It is more an urgent reasonableness that sets the tone for Déjà Vu, a film that chronicles Young’s tour and also features scenes from Iraq and interviews with war veterans and their families.

There are flashbacks to Vietnam-era protests and a younger, hairier CSNY. It may lack the passion of Michael Moore’s Fahrenheit 9/11 but with the pathos of some of its war stories, it rises to an elegiac wistfulness.

The rasping whine of Young’s singing voice and the plaintive urgency of the songs (thankfully, the music gets much better as the tour goes on) are a fitting accompaniment.

I meet Young in an old roadhouse above the Pacific Ocean, where the golden late-afternoon light filters through tall redwood trees.

His battered 1950s Plymouth saloon is parked outside the entrance. The log building is empty apart from Young and two ageing Los Angeles music industry minders.

It seems the perfect setting; a place left marooned when — to borrow Joan Didion’s phrase — the tide of the 1960s went out.

When I ask whether this anti-war work isn’t better left to a younger generation, Young agrees.

“I was hoping some young person would come along and say this and sing some songs about it,” he says, “but I didn’t see anybody. So I’m doing it myself. I waited as long as I could.”

Young’s involvement provokes inevitable comparisons with the Vietnam protests but the innocence and anger of that period have been succeeded by the sophisticated cynicism that is the standard reaction to Iraq.

Asked whether protest music still has a way to touch the emotions of a mass audience, Young doesn’t duck the question: “Not really. If it does, it seems to be doing it in a context of history. It’s not a real communication.”

The average age of the band members (62 and a half) probably has something to do with it, Young says.

But it also reflects changes in the times. “The world is so different and the audience is not unified by a threat,” he says. “That’s the big difference between the 1960s and now. There’s no threat.

“ ... people criticise this generation for not being with it, not being alive, not being cognisant of what’s going on in the world; it’s because they’re not affected directly by it,” he says.

“This generation is just as sensitive as the 1960s generation but they just haven’t been tickled yet.”

The media take their hits blamed for the overkill that have combined to stultify the American public.

“It’s repeating itself endlessly,” he says, “like a giant machine that just spews out the same stuff over and over and over again.

Twenty-four-hour news really screwed things up.”

But Young’s isn’t the only anger portrayed in Déjà Vu. The other side gets a chance, too.

It comes in Atlanta, Georgia, when CSNY break into the jaunty chorus from Let’s impeach the President, a protest song that doesn’t pull its punches.

The sentiment doesn’t go down well with many in the crowd, who probably thought they were coming out for a nostalgic evening reliving Four Way Street.

The booing grows louder and people start to leave.

Young suppresses a chuckle at the memory, then embarks on a rather unpersuasive attempt to argue that his film was really trying to present both sides of the issue. “It doesn’t exclude these people; it tries to respect them,” he says.

At least the music finally touches a nerve. When Crosby gets back to his feet and hits a stirring guitar solo, the tour starts to make sense. “It took a while to get going but the music on the record is really good,” Young says. As a last hurrah, there is a sort of shabby nobility to it all.