Thirty years later, he plans to complete this weekend's 10-kilometre course in less than 80 minutes.

Mr Ion, from Surf Beach on the NSW south coast, turns 80 on Thursday, and will have more than 15 proud supporters wearing "Grumpy Old Man Support Team" T-shirts, including his great-granddaughter, Annika, 2.

Surprisingly, he only returned to running a few years ago.

After finishing the 1985 event within 120 seconds of his 50-minute target, he stopped running until his doctor recommended exercising to lower his blood pressure five years ago.

"Exercising" meant walking, but Mr Ion felt that "walking took too long", so he lifted his goal for this year's event.

"I finished the Fun Run in less time than my age 30 years ago and thought I'd try again. It became about running with the dog instead of walking . . . but it's only the past four months I've been taking it seriously," he said.

The first time, Mr Ion ran the 10 kilometres in one hour 45 minutes. However, he has a good chance this weekend with a record time of 76 minutes.

"I'm still not confident, circumstances change. I know there are some uphill sections in it, so time will tell."

His granddaughter, Amy Yates, a physiotherapist, said the benefits of remaining active at an older age included improving muscle and bone strength, preventing or delaying disease and improving mood.

Mr Ion said he felt healthier and his bone density had increased 10 per cent.

"I don't think it's ever too late to get started," he said.

"At first, you get tired, breathless and unmotivated . . . But I certainly feel a great deal better than before. You find muscles you didn't know you previously had."

He had hoped to raise $400 for Team Cure Brain Cancer, in honour of a family friend who passed away.

However, he is thrilled to have raised $945 and hopes to hit the $1000 mark by Sunday.

He also hopes the 80-year-old who won last year's 80-plus category has "had enough" so he doesn't finish second.

And if he doesn't reach his goal?

"I'll try again at 90 and take advantage of the extra 10 minutes," he said.

Correction: An earlier version of this story said Mr Ion was from Hackett.