“Just because no one has lived forever before, doesn’t mean Nan won’t be the first.” That’s a joke my cousin made about my then 94-year-old grandmother. A decade later it feels more like a prophecy.

Nan is 104. She’s lived on her own for more than 30 years, remains sharp between the ears and maintains her hair appointments religiously. Whenever I mention her age the reactions are the same eye-widening universal amazement – yet it still catches me off-guard. Apparently this isn’t normal. Not everyone’s grandparent has a letter from Queen Elizabeth II.

She was one of the thousands of schoolchildren who walked across the Sydney Harbour Bridge days before its official opening in 1932. She still has a head full of steam over the removal of Sydney’s tram network in the early 1960s. When she neared 90 I headed overseas for 12 months. We had a tearful goodbye thinking it might be the last. She made a fool of both of us.

People want to know her secret to a long life. But to understand her longevity, you have to know more about the life she’s lived.

Nan, or as she was known in her early years, Coral Giddy, was born at the tail end of the first world war. She left school as a teenager and joined the workforce in a garment factory to support her widowed mother. She married Pop and raised a child on her own while her husband was fighting in Papua New Guinea and Bougainville during the second world war. Her three children gave her six grandchildren. She became a great-grandmother 23 years ago and has 10 great-grandchildren at last count. When the governor general met her at a shindig for centenarians, he told her she was remarkable for her age. Her response was to let him know she still showers herself – although she still can’t explain why she said it.

Jokes about living forever aside, I have sat down with her and started documenting her life on camera. I’ve had the great fortune of being able to turn to her for wisdom and advice and want the same thing for the younger members of the family.

So we talked about her early dates with Pop, to the long-demolished Tivoli theatre and the expensive box of Winning Post chocolates he bought her. How he sent over jewellery he fashioned from scrap material and bullets during the war. She spoke about feeling like an outsider moving to Wollongong and how the migrant communities there introduced her to wine. She says the inner-city suburbs where I spend most of my time were considered slummy when she was younger. I reminded her she could have bought an entire street of houses for the cost of two pizzas.

Then came the question about living to 104.

She says it comes down to genetics and finding the right partner. She was widowed more than 30 years ago and says the life she built with Pop has supported her since. It helps to remember your pills, she adds, and to get up, shower and make your bed every day.

I suspect the truth about her endurance is something different. Nan is determined to keep her eyes focused on the future. Even when days are hard, she still looks forward.

That’s how, at 98, she moved nearly 1,000km from Wollongong, her home of 60 years, to Melbourne. She tells me she made the decision only a few weeks after my dad died, 15 months after being diagnosed with cancer. She was on her balcony, staring out over the city and the Pacific Ocean, and realised she had everything she wanted in the world right there, except him. She had to move on.

Nan still struggles to talk about Dad and his death. She can recall intimate details about so much of her life but her heart won’t let her open up on that chapter. She doesn’t love what she’s left behind any less but experience has told her life only travels in one direction and you need to move with it.

A life as long as hers can be hard to comprehend. Asked what the biggest change to the world she had seen across her life was, Nan replied that it was television. Life when she grew up rarely extended past her suburb. Television connected the living room to the world.

A few days later she said she’d correct her answer if she could. She thinks the pill shook things up and that it was a great thing. She’s a feminist who knows she’s on the right side of history – not just because she’s seen a lot of it.

When I mentioned to her that I wanted to write about her life, her response was typically modest. “You should write about your other grandmother,” she said, meaning the one who moved to Australia from Scotland as a widow with 10 kids. She spoke of my gran’s wisdom and headfirst approach to any challenge she met. She called her resilient.

And maybe that’s her own secret to a long and rich life. Not many living people can say they lived through two world wars, two pandemics and outlived a husband and a child. Even fewer would still look forward to the next day but that’s what she does. She’s one of a kind, my nan. 104 years young and always thinking of tomorrow.