He would run five kilometres.

In 2018, Mr O'Meara went even further and completed The Canberra Times' half-marathon.

Since then he's laid back and taken it easy - by taking on "six to eight" full marathons and an ultramarathon.

Mr O'Meara got quickly bored while undergoing radiation in Canberra, his partner Allison Allwood said.

"He doesn't read or watch TV, he doesn't like sitting still, basically. He was really bored up there. So he started walking; the walking turned into jogging," she said.

Running feels like "freedom", Mr O'Meara said.

Despite the cancer prognosis, Mr O'Meara is unbelievably fit.

"It's bloody amazing. He ran the Stromlo 50km trail run last November. It was just amazing," Ms Allwood said.

"He comes up after the marathons, and most people are just collapsing [but] Timmy walks 2km home to where he's staying. It's extraordinary."

Aside from running three times a week and going to the gym, Mr O'Meara mows lawns in order to fund his hobby.

Mr O'Meara will be running 42.2km at The Canberra Times' marathon festival on April 7.

Prostate cancer was likely the most common cancer in males in 2023, accounting for nearly one-third of all diagnoses.

While there is no single test to detect it, the prostate specific antigen (PSA) blood test can indicate the possibility of the cancer.

Mr O'Meara said he had taken the blood tests for several years before his general practitioner noticed an elevation off his baseline.

He had an aggressive form of prostate cancer which Ms Allwood said would not have caused symptoms until it was too late.

"If not for the blood test, he would not have shown symptoms until he was stage four. Just that small dip into the PSA and the doctor [was] getting on to it really early," she said.

"Not all cancers impinge on the urethra, so you don't get any urinary symptoms until it's there.

"If we hadn't gotten into on to it very early, Timmy would be in a very different state now."

Mr O'Meara wants all men to start getting their prostate specific antigen blood levels tested.

"Hopefully this will get people to go and be checked," he said.

Prostate cancer mostly affects people aged 50 and above.

After non-melanoma skin cancer, it is the most common cancer in Australian men.

There is a 96 per cent five year survival rate.

The Cancer Council says that while an elevated PSA can indicate prostate cancer, "two-thirds of cases... are due to noncancerous conditions".

"Overdiagnosis of prostate cancer can lead to unnecessary treatments that have side effects such as sexual impotence, urinary incontinence and bowel problems."