Cahill, 35, will be a key player for Australia at the Asian Cup on home soil next month, with the men in green and gold still reliant on their veteran talisman for goals.
Australia coach Postecoglou had previously suggested the former Everton forward would unlikely to be around when the next World Cup kicks off in Russia in 2018 but Cahill this week claimed he felt capable of continuing until 40.
"I'd be delighted if he's still banging goals like he is now in four years' time," Postecoglou said.
"If you go on the evidence of the last 12 months, particularly in international football, Timmy's still a world class striker. If he continues in that form it's fantastic for us.
"Timmy's a very important part of what we're doing and what we're building. Not just on the field but off the field too. He's been a fantastic leader for this young group in the last 12 months."
Cahill, along with Mark Bresciano, is one of just two survivors from the 'golden generation' that took Australia to the 2006 and 2010 World Cups, a group of players Postecoglou has been accused of - in some quarters - forcing into retirement.
But the national team coach has insisted players are free to make their own decisions on international availability.
"I don't think I've called an end to anybody's career," he said.
"All I do is select squads and then people make decisions beyond that.
"Certainly it's not up to me to tell people when their career should finish."
A key factor in determining Cahill's longevity will be his next destination in club football.
The ex-Millwall man has one year remaining on his contract at New York Red Bulls and has been linked with a move away from Major League Soccer, with the A-League beckoning as a dream destination for Australian football fans.
"The pleasing thing for me is he makes these decision on the back of [the fact] he wants to prolong his international career," Postecoglou said.
"He'll make a decision that he thinks his best for him to continue wearing the Australian shirt. Which I think is fantastic, the fact he's willing to put his country first. He's a pretty smart cookie, he's probably smarter than me when it comes to making the right moves.
"So I'd back him to make a good move again."
