By Vincent Dowd
BBC World Service arts reporter
Dropping yet more sugar into his cafe mocha, Pete Seeger laments the withering of his singing voice: "At my age the banjo-playing is shot too".
In fact musician Seeger often seems 20 years younger than he is - although these days what excites him is less his music and more the well-being of the US environment.
Seeger has inspired many younger US artists and songwriters
But this weekend he will quit the Hudson Valley for his native Manhattan and a big concert to celebrate his 90th birthday.
On the bill are Bruce Springsteen, Baez and more than 30 other names.
Affection for Pete was not always so widespread.
In the 1950s he was blacklisted for his former membership of the Communist Party, and his performing career seemed all but over.
Typically, he refused to go away. In 1955 he declined to co-operate with the Un-American Activities Committee which was investigating radical activities of public figures.
Not saying sorry
He was sentenced to a year in prison for contempt, although a smart lawyer spared him imprisonment.
I asked Seeger if he ever came to resent his country in what he calls "the frightened fifties".
"America's treated other people much, much worse. I've spoken frankly about once being a member of the Communist Party. Should I apologise for it? Well, a lot of apologies are due.
"White people in the US should apologise to native Americans for stealing land - and to African Americans for slavery. Europeans could consider apologising for centuries of worldwide conquest. On the other hand, let's look ahead!"
Seeger's music has always had a political edge
His energy and optimism is characteristic. He remains as fascinated by the world as he must have been as a young man when he dropped out of Harvard.
Seeger came from a prosperous middle-class family but was inspired by the singer Woody Guthrie, seven years his senior, to explore America's folk tradition.
He was a member of the left-wing group The Almanac Singers and then had mainstream hits with The Weavers.
Songs he has written, adapted or collaborated on include Where Have All the Flowers Gone?, Turn Turn Turn, If I Had a Hammer, Bring 'em Home and We Shall Overcome.
In January, he performed alongside Bruce Springsteen at US President Barack Obama's pre-inauguration concert in Washington. He sang Woody Guthrie's This Land is Your Land.
The choice shows Seeger has radical credentials even now.
"Bruce got in touch with me - I never would have gone in for all that hoopla down there if it wasn't for him!" he says.
"He knew I like to sing those verses in a particular order: 'There was a great high wall there that tried to stop me/ There was a great big sign there said Private Property/ But on the other side it didn't say nothing/ That side was made for you and me.'"
It is Springsteen who has done most to bring Pete Seeger to younger music fans' attention - especially with his 2006 album The Seeger Sessions.
So does Seeger feel he is living in a different America as he hits 90?
"It's slowly but steadily been changing through the decades. The danger now is people say, 'Oh, we can relax and let the new president do the work.' The most important part of Obama's inauguration speech was when he said WE have to do the job - all of us!"
Despite his outsider image, Seeger has been welcomed into the fold
Pete Seeger was a supporter of Martin Luther King and sees a line connecting him to the new man in the White House.
"In 1965, my wife Toshi and I got a telegram from Dr King inviting us to join the rights march from Selma to Montgomery, Alabama. There were maybe 300 of us, sleeping in big tents. It was raining half the time and our feet were covered in mud. But we were singing all the way!"
Seeger has always believed words and music will help make society better.
In part, the New York concert is an apology for how the US once treated him - though Seeger would be the last person ever to seek such a thing.
But also it is a celebration of a long life founded on courage and hope - and on the power of popular song.
Vincent Dowd presents Archive on 4: Pete Seeger at 90
on Saturday 2 May at 2000 BST on Radio Four (the programme will be repeated at 1500 on Monday 4 May).