"It's proven to be true. I still say 'Never say never'. It's not over until it's over."
Schwarzer will be 41 in October, but has the 2014 World Cup in his sights and believes he is playing as well as ever.
"I am 40 years old but I feel incredibly well and I am holding my own, no problems whatsoever," he added.
"I feel incredibly fit and I love playing football. As long as I am playing well enough at this level I will continue to play.
"The aim is to continue to get better; I don't want to stop getting better.
"If you stop getting better then it is a downward slippery slope."