If you have watched Roger Federer playing tennis in the last few months, you would struggle to accept that the Swiss star is 33 - perhaps it's only the wrinkled forehead lines that give it away.
He's at the age now where many tennis stars may be considering hanging up their racquets. However, his former coach, Tony Roche, believes that the 17-time Grand Slam champion still has four to five years left in his professional career - that would take him to 38, just two years shy of 40.
The timing of Federer's future retirement is a constant hop topic around tennis and the player himself has given no such hints as to how long he may continue.
At the moment it would seem there is no chance of the world no.2 calling it quits. A terrific end to 2014 saw him narrowly miss-out on regaining the world no.1 spot from Novak Djokovic who, in the end, proved to be too consistently good in securing a hat-trick of ATP Finals titles in London. Federer was forced to skip their finale through injury.
The disappointment of missing out on a seventh Tour Finals title in London was more than banished by Federer, however. One remaining piece of silverware that Federer hadn't lifted, the Davis Cup for Switzerland, was finally secured recently against France.
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With literally every significant honour now bestowed upon him - Grand Slams, Masters, Tour Finals, Olympics & Davis Cup - the question now is of Federer's motivation to keep going.
Roche doesn't think that there will be a personal struggle though: "I think he can play as long as he wants to on the mental side. Physically, I think he can play for another four-five years without any problem," he told 'The Times of India'.
Roche, now aged 69, worked with Federer for two years between 2005 and 2007, a time where the Swiss star started conquering the sport. They came together because of Roche's expertise on the clay-courts, having won the French Open in 1966 in the singles and two further occasions in the doubles.
Of course Federer went on to become the sport's most successful Grand Slam player by winning 17. And, despite a two-year drought, Roche reckons his former student can get to no.18 and that he will be remembered as tennis' best-ever.
"Another Slam definitely... Obviously, Wimbledon is his best chance but he's knocking on the door in last few Slams. As long as the guys still respect Roger, he is always going to be a threat," continued Roche, who has also coached Ivan Lendl and Lleyton Hewitt.
"Roger is the most talented player to ever play the game. Working with Roger was a little bit different. I introduced Roger to harder practice sessions to not only rely on his talent but to put in the hard work. We worked a lot on his second serves and volleys."
We have a little wait before we can see Federer attempt to finally bag that elusive 18th title. His next opportunity will come at January's Australian Open, a competition he hasn't won since 2010 - his 16th of 17 titles in-total, to date.
For now the world no.2's focus is on the International Premier Tennis League. Federer is due to play his first match for the Indian Aces soon.