Australians could be older than they think.

Researchers say they can measure the biological age of a person's brain and organs, challenging the belief that age is determined by your date of birth.

And it's good news for those who might show signs of early ageing - with researchers claiming early intervention is the key.

In a study published in Nature Medicine, Dr Ye Ella Tian, the lead author from the University of Melbourne's Department of Psychiatry, and colleagues demonstrate how a person's chronological age might differ from their biological age.

The team looked at brain and body systems including heart, lungs, bone and muscles, kidneys, liver, immune and metabolic functions in more than 100,000 adults who took part in a UK Biobank study.

"Your age is not solely determined by your date of birth, and your heart's biological age is closely linked to the age of many other body systems," Dr Tian said.

"So, if your heart appears older than your chronological age, it is more likely that your kidneys, lungs, bones and brain will also appear older.

"It is important to keep your brain and body young because advanced biological age is a potent predictor of disease and mortality."

Professor Andrew Zalesky said researchers were able to use various types of brain imaging data, information from blood samples and other physiological measures to determine the age of a person's organs.

"A lot of the biomarkers and measures are already routinely clinically used - so they can be measured in that sense," he told AAP on Monday.

"The idea (going forward) is not to test individuals, but our aim is to test people who have a predisposition or an existing risk that would mean measuring organ age could give medical professionals the insight to commence early treatments and interventions."

Participants who took part in the study were aged between 37 and 73, some with chronic health conditions.

"In the future, we hope that the biological age of your brain and body will be routinely measured in the doctor's clinic to identify people at risk of chronic disease," Dr Tian said.