Dr Popovic said language affects our cognitive function and we talk ourselves into the idea that we cannot do things because we are too old.
"If we replace the word 'can't' with the word 'how' it arouses our curiosity and curiosity stimulates our brains.
"I stayed with my father recently, he is diagnosed with vascular dementia and I set up two jars - one for me and one for him and every time he told me he couldn't do something, he had to put some money in my jar.
"When he said he could do something, he got money back in his jar, it was a great motivator for him."
With her blog What's Up Doc and question and answer column Prescriptions as well as her seminars and workshops, Dr Popovic has attracted a large following in Australia.
People can work well into their 90s and it's not about genes, she said.
She gave examples of American architect Frank Lloyd Wright, who designed his last building at age 90, and New Zealand solicitor and judge Sir Trevor Henry who remained active in New Zealand law well into his 90s.
"We can stay as sharp at 90 as we were at 30 if we want to, it is not restricted to a genetically-lucky few."
Dr Popovic graduated from Sydney University medical school in 1995 and has worked as a lifeline counsellor, fitness instructor and runs a number of public programmes throughout Australia.
She told TV3 last year that although people can have a genetic disposition to dementia, that doesn't necessarily mean they will get it.
