"I'm 46 years old and occasionally I have a hard time putting my shoes on in the morning," Agassi said in an interview with CNN in Umag, Croatia in July, where he played his old friend Goran Ivanisevic in an exhibition event. "No question that my body is older than its years."
The transition from professional athlete to retiree can often be challenging and the American realized he had to find a new focus once he stopped playing and he's now devoting most of his time to his new passion: building schools in the United States.
Agassi's wife and fellow multiple grand slam winner, Steffi Graf, runs a foundation aimed at helping children who have been traumatized by war or violence.
The way he has adapted to life away from professional tennis is a source of pride to Agassi, especially as the prospect of retirement had filled him with dread.
"It's like preparing for death," said Agassi. "Nobody knows what it's going to feel like and nobody knows when it is going to happen and when it does, it's your time."
Yet retirement also came as "a relief," said Agassi, who lives and works in Las Vegas with his family -- he and Graf have two children -- and devotes most of his time to education. "I had accomplished what I wanted. I pushed myself as far I could go."
Coached by his father Mike, a volatile former Olympic boxer from Iran, Agassi was a child prodigy who grew up playing hustle matches in Las Vegas.
In his 2009 autobiography "Open" Agassi recalls Mike Agassi once pointing a handgun at another driver while he was in the car and remembers beating former NFL star Jim Brown at the age of nine to win a $500 bet, arranged by his father.
Having taken the tennis world by storm as a young upstart with long hair, denim shorts and lightning-quick reflexes and footwork, Agassi wrote in his autobiography that at times he hated tennis "with a dark and secret passion."
He regained his love for the game in his late 20s and would leave the sport as one of its most popular competitors and most eloquent spokesmen.
'Athletes die twice'
With 35-year-old Roger Federer out for the rest of the season with a knee injury, Serena Williams turning 35 next month and her sister Venus aged 36, there has been speculation that tennis may see a spate of high-profile retirements sooner rather than later.
"I don't think there is a right moment to retire," Agassi said. "The truth is that athletes spend a third of their career not preparing for two thirds of their life."
After dedicating their entire existence to getting an edge, athletes can hit a brick wall once they retire and have to get used to life on the outside where the highs and lows of winning and losing are less pronounced.
U.S. baseball star Jackie Robinson once famously said: "athletes die twice," the first time being the day they retire from playing elite sports.
The likes of four-time Olympic track champion Michael Johnson and former Wimbledon winner Pat Cash have thrived in their new roles, working in the media and in the case of Johnson, opening his own performance center for young athletes.
Yet there are plenty of athletes who have struggled.
Former England footballer Paul Gascoigne's problems with alcohol addiction since his retirement are well-documented while Australian swimming star Ian Thorpe struggled with depression and alcohol abuse during and after a brilliant career that earned him nine Olympic medals.
In an interview in 2014, British two-time Olympic track cycling champion Victoria Pendleton said she missed the regimented structure professional sports had given her in retirement.
The 2016 US Open is the 10th anniversary of Agassi's memorable retirement, when he lost to Germany's Benjamin Becker on September 3 after struggling through the first two rounds with a bad back which required a cortisone injection and three anti-inflammatory shots.
After a four-minute long ovation from the crowd at Arthur Ashe Stadium, an emotionally and physically drained Agassi paid tribute to his New York fans, telling them: "The scoreboard said I lost today, but what the scoreboard doesn't say is what it is I've found," as tears rolled down his face.
"Over the last 21 years, I've found loyalty. You have pulled for me on the court and also in life."
Has Serena underachieved?
Although Agassi's day-to-day commitments don't leave him much time, he said he follows tennis when he can and is most impressed by Novak Djokovic and Serena Williams.
The top-ranked Djokovic will bounce back from his Wimbledon and Olympic disappointment to win the US Open, Agassi predicted.
The Serb's shock third-round defeat by American Sam Querrey ended his hopes of a third straight Wimbledon title and ruined his chances of becoming the first man since Rod Laver in 1969 to complete the calendar year grand slam.
He then was knocked out of the Olympic tennis tournament in the first round by eventual silver medalist Juan Martin Del Potro.
Andy Murray went on to win his second Wimbledon title before successfully defending his Olympic title in Rio and many are tipping him to claim a second US Open victory.
But Agassi says Djokovic is still the man to beat. "He will come back for the US Open," he said.
"Anybody that knows me knows that I think he should win everything all the time," said Agassi, a two-time champion in New York. "That is how he separated himself from everybody."
Agassi is equally impressed with Williams, who tied Graf's Open era record of 22 slams at Wimbledon and will overtake the German if she wins her seventh US Open.
"It's remarkable," Agassi said. "I've kind of joked for a long time, quite frankly that she is probably one of the only persons I've ever seen that, no matter how much she wins, she could always be considered an underachiever.
"Because I remember years when all of a sudden she didn't and you're going: 'Why didn't she?' She's so good."