But the Proclaimers have warned their army of fans they are prepared to walk away from performing live.
Speaking in a new BBC Scotland documentary, the Edinburgh-born twins say they will quit if they believe they are no longer as good as before.
Charlie Reid said he and his brother will “not need to be told” when to call it a day, adding: “The trick is to know when to call it a day.”
In the programme, to be screened on Wednesday on BBC2, the Proclaimers reveal that royalties from their most popular anthem, I’m Gonna Be (500 Miles), is helping them release new albums and tour the world nearly 30 years after it was released. They have pledged never to drop their biggest hit from live shows, fearing they would “not get out alive” if they refused to play it.
First Minister Nicola Sturgeon credits the Proclaimers with helping to fire her interest in politics as a teenager with their first hit single Letter From America, the lyrics of which feature her home town of Irvine.
The Reid brothers, who turned 55 this year, were interviewed by actor and diehard fan David Tennant for the documentary.
Charlie Reid said: “Some people quit too early and some people go on too long. The trick is to know when to get out. If you are no longer up to muster you should quit. I know we will. We will not need to be told.”
Craig Reid said: “We express ourselves through our music and we do it to the absolute best that we can. Life is short. You never know when it’s going to end. You’ve got to give everything you’ve got.
“Sometimes you get nerves (on stage) and you don’t know why it’s happening. It’s always good to have that. You should never be on autopilot at all. The energy should be going through you. That’s what’s going to communicate what you’re thinking and feeling to the audience. If you keep delivering I think people will keep coming back.”
Recalling how the song I’m Gonna Be (500 Miles) came about, Craig said: “The song was written when we were touring with the first acoustic record. We were playing up in Aberdeen. I was getting picked up in an hour.
“I sat down at the electric piano and started playing and it came in about 45, 50 minutes, the whole lot. It was one of the quickest songs I’ve ever written. It was like it was writing itself.”
Charlie added: “It (the song) is the reason we’re able to carry on making records. In terms of what it’s brought in over the years, it pays for new records, it pays for tours, it underpins everything we do. I don’t know what it is. Something about it is indestructible.”
The First Minister, who joined the SNP when she was at school, recalls the impact made by Letter From America, which tackled the impact of rising unemployment in 1980s Scotland.
She said: “Letter From America came out at a time when I was getting really involved in politics. It wasn’t just that my home town got a mention in it, but it was also that it spoke about something about my country that was also motivating me to get involved in politics. That song, for me, is the anthem of my teenage years.
“Their songs over the last 30 years have been the soundtrack to Scotland’s political journey. That has made politics much more accessible at times to younger generations and brought politics alive. In very simple terms, but also beautifully lyrical terms, telling Scotland’s story in that way was really important, politicising a generation of young Scots like me.”