However, his form over the past year has given no indication that his career may be on the wane.
"By no means am I going to close the door. No way," said Mortlock, who currently has 74 international caps to his name.
"I'm not one who lacks energy but I guess this season has given me a resurgence in my enthusiasm levels."
The Wallabies bring the curtain down on a long season at Wembley this evening, with Mortlock having thoroughly enjoyed his rugby in 2008.
"Last year, coming off the World Cup, was a big disappointment and I had to make a decision on where I wanted to go.
"And as soon as I made a decision, it gave me a huge amount of drive and passion to hopefully be part of the renewal process and I've just been loving it. I've been up the whole time.
"I'm thoroughly enjoying being associated with footy. The environment is really conducive to that and this group of guys are a great bunch of guys to be a part of.
"Maybe in a year or so it will be time to sit down and hopefully my form and everything are in the right shape. (Mortlock's contract with the Australian Rugby Union comes to an end in 2010.) If they're not, so be it. But I will be doing everything in my power to make sure they are."
Mortlock's recent performances have drawn substantial praise from new Wallaby coach Robbie Deans, with the Kiwi in no doubt that his captain can continue impressing for the foreseeable future.
"Stirling's getting younger by the day," Deans told AAP. "I wouldn't limit his rugby life span.
"You've only got to look at games this year. He's at the thick of everything that happens.
"When you look at the amount of leadership we've lost this year, in terms of historical leadership - Gregan, Larkham, Latham, Vickerman, Elsom - it's been important to us to have blokes like Stirling who understand the arena, understand what's required. Not only in terms of playing but also in terms of preparation. He loves the occasion."
Mortlock has started most of his recent rugby at inside centre having been more used to wearing the No13 shirt under previous national coaches. Deans believes that move is one of the reasons why the ACT Brumbies star is playing better than ever.
"He's really enjoying his rugby and I think he's quite enjoyed the challenge of the positional switch.
"It's brought with it some different requirements in terms of time and space and skill set, but he's enjoying being extended.
"It's probably advantageous from a leadership perspective as well. Being a bit closer to the action, allows him to get involved and inspire."