Shortly before he turned 65, Bob Cheek took a plane to the US and turned up at a 24-hour gym in California. He had read about this new type of gym in a magazine, back in Australia, and ended up outside one in San Diego, wanting to see how they were run. He knocked on the door; a man opened it and told him he couldn’t come in because he wasn’t a member. “I said: ‘Can you just talk to me about this gym?’”

The man explained how it was run – that it was only supervised sometimes, and members could let themselves in at any time – and Cheek was sold. “What a great idea,” he says, smiling. He couldn’t wait to get back to Tasmania to open one. He already had a gym – a high-end, loss-making one. “So I had to do something.”

Cheek had enjoyed a varied career. He grew up on his parents’ farm in northern Tasmania, then became a professional Australian rules football player. When that career was coming to an end, he switched to journalism, becoming editor of a paper in Tasmania. He also “dabbled in a few things in business”. While many of his footballing peers went into running pubs, he was more interested in fitness, and invested in gyms “with varying degrees of success”. As he complained to a friend that politicians didn’t understand the pressures small businesses were under, “My friend said: ‘Put up or shut up.’” So in 1996, Cheek stood as an MP for the Liberal party and was elected to the Tasmanian parliament, becoming leader of the opposition in 2001 before losing his seat the following year.

He came out of politics without a big pension, with a failing business, and wondered what to do next. “That’s a very good incentive to get going,” he says. “I wanted to keep doing things with my life anyway. I never thought of myself as old – age has never worried me.” When we speak over Zoom, Cheek, 78, is in a hotel room in northern England, having cycled over the North York Moors that day, on a cycling trip that will eventually take him from Dublin to Copenhagen. “It’s just a challenge,” he says.

He borrowed money to put into opening his first 24-hour gym in Hobart, Tasmania’s capital. “It was a risk. If it hadn’t worked out, I probably would have lost my house and everything else.” It was a struggle at first, he says, to get the local government officials to agree to it. “Twenty-four-hour gyms were unknown. They thought they were going to be the headquarters for drug distribution and murders. They couldn’t believe that people were going to go in at night and there would be no supervision.”

The first opened in March 2009, and Cheek knew from the start it would be a success. It was far cheaper than most gyms and appealed to a wider range of people, including those who worked shifts and wanted to exercise at less common times. He says 700 people joined before it even opened. “I went into the car park that first night and saw it packed, and it was just an incredible feeling. So we kept building them.” He built more in Tasmania, then started in mainland Australia, usually taking over old video rental shops – their open-plan layouts made them ideal – which were going out of business at the time.

Cheek, who has three children and several grandchildren, ended up owning 37 gyms across Australia, with plans to move into south-east Asia, and he loved it. Most of the members were under 40, and he says “it kept me young, too, being involved with all these younger people coming in. Gyms are the new meeting places for young people. In my day, everyone went to the pub; now they go to the gym. It was great seeing all these young people getting fit and having a good time, and older people as well. And, I’ll be honest, I was making a good quid too.”

In 2017, he sold the chain for a reported $50m. He didn’t particularly want to and had turned down offers before, but he was having some issues with investors and was in his 70s by then, and people kept telling him they were amazed he wanted to keep going. “I had seller’s remorse for a long time,” he says, until the pandemic hit and he felt lucky not to be running gyms. But he still misses the business.

“It gave me a new lease of life,” he says. “My life has got better as it’s gone on: my 60s were one of the best decades of my life, and I think my 70s are even better. I know health can have a big say in that, but for me it was like a magic carpet ride, flying into my 60s. I didn’t even feel it – I felt like I was 35 again – and that’s about having a sense of purpose, building something and helping people. I worked really hard, but I loved it.” He smiles, happy even if he complains about his back and neck from a gruelling day cycling Yorkshire’s hills. “I’m looking around for the next thing now. I can’t go riding bikes for ever.”

• Bob Cheek has written a memoir, Dumbbells to Diamonds

• Tell us: has your life taken a new direction after the age of 60?