City2Surf 2019: Wagga Road Runners athlete Heather Lillington, aged 76, to take on one of the state's hardest marathons

It will be the furthest she has ever run, culminating her lifelong "healthy hobby".

"Since I was a little girl, I've always loved athletics. I was always running when I was at school," she said.

"My dad was a state cricketer, so he used to encourage me a lot. But of course back then we didn't have coaches like we do now."

Her track ability earned her the schoolyard moniker of 'Marjorie Jackson', in honour of the former Olympian.

When she crosses the line to end Sunday's marathon, her personal achievement will be bolstered by having completed the race along with her two granddaughters, 16-year-old Jade and 14-year-old Claire.

Both the teenagers will complete with a team from The Riverina Anglican College.

Ms Lillington has been training with the Road Runners since relocating to the city two years ago.

"Linking in with the group was the best thing I could have done. Having them believe in me helps me to know I can do it. The thing is, when I get out there I feel 18 again."

When she returns from Sydney, Ms Lillington will continue training for her third attempt at the Lake Run and Ride, as well as the Pomingalarna Trail Marathon.

"I've done [the local races] a few times and picked up a gold and a silver in my age group, not that there's many in the 70-plus section. I don't do it to win, but it feels good."