When Caroline Wozniacki, world No 1 at the age of just 21, is repeatedly asked why she has not yet won a Grand Slam title, it is no wonder that Maria Sharapova is regarded by some as a veteran. After all, it is four years since the Russian last won a major title and eight since she stunned the tennis world by winning Wimbledon. Petra Kvitova, the current Wimbledon champion and the world No 2, is another 21-year-old, while Victoria Azarenka, the only other player above Sharapova in the world rankings, is also 21.
If 24-year-old Sharapova has become as established a part of the tennis landscape as Hawk-Eye and sliding roofs, it is because she is one of only two teenagers to have won a women's Grand Slam title since the turn of the century (Svetlana Kuznetsova at the US Open in 2004 is the other). Sharapova triumphed at the All England Club less than three months after her 17th birthday, making her the third youngest Wimbledon singles champion in history.
As she prepares for next week's Australian Open in Melbourne, where she won her most recent Grand Slam title, Sharapova is well aware that time never stands still, least of all in women's tennis. "I've been a professional tennis player since I was 13 or 14 years old, and I achieved big things when I was quite young, so I think that's part of the reason why it feels like I've been on the tour for so long," Sharapova said. "Someone was saying how young Petra [Kvitova] was – and she's 21. I was thinking to myself: 'Oh my God, 21, what does that make me? I'm like a grandma!' But I'm just three years older than her."
The fact Sharapova has not won a Grand Slam title for four years has nothing to do with any weakening of her passion for her sport, and everything to do with the physical demands it has placed on her body. Within weeks of her 2008 triumph in Melbourne she was having trouble with her right shoulder. That summer she lost to Alla Kudryavtseva, the world No 154, in the second round at Wimbledon and by October she was undergoing surgery.
It has been a long and frustrating route back. Sharapova did not play a singles match for nine months, had to remodel her service action and seemed at times to struggle just to keep the ball in play. In the 22 months from April 2008 she won just one tournament. In 10 Grand Slam appearances her best performance was a single quarter-final in Paris.
Nevertheless, Sharapova never gave up hope and continued to work on her game and her fitness. She appointed a new coach, Thomas Hogstedt, and at last her dedication began to pay off last year. She played in her first Grand Slam semi-final for more than three years at the French Open and followed that by reaching the Wimbledon final for the first time since 2004 before losing to Kvitova. Her season petered out because of an ankle injury, which also forced her to take the precaution of pulling out of last week's Brisbane International, but she has been practising for the past week in Melbourne.
Like most players, Sharapova loves the first Grand Slam tournament of the year and the sense of optimism surrounding it. "I don't know if it's just the [fact that it's] summertime in Australia and everyone seems to be in a really great mood," she said. "I love Australia altogether. It's one of my favourite places to visit. There's just such an easy-going feel about it. The fans are just very enthusiastic, and when you feel that energy in the atmosphere and the crowd I think that brings the best out in us."
Does the event always feel like a new beginning? "It does. It's like a test tournament in a way, because for us, a month-and-a-half of an off-season is a long period of time. In a way you're seeing where you're at, seeing the work that you've put in, how you finished the year and what you took out of that, and how you incorporated that into practice and how you brought it on to the court. Yes, I think it's a good test."
If Wimbledon 2004 remains Sharapova's most treasured victory, her win at Melbourne four years later was arguably her most emphatic. Winning the title without dropping a set, she beat Justine Henin, the then world No 1, in the quarters and also swept aside three former or future No 1s: Lindsay Davenport, Jelena Jankovic and Ana Ivanovic.
Can Sharapova win again this year? The tournament looks wide open. Kim Clijsters and Serena Williams, the last two champions, both returned in Brisbane after lengthy lay-offs only to pull out with injuries. Kvitova can look vulnerable on outdoor hard courts and the Grand Slam credentials of Wozniacki and Azarenka remain open to question.
Given her recovery from the shoulder injury, Sharapova said that winning another Grand Slam title "would definitely be the biggest victory in my career, knowing what I had to go through in order just to play tennis, mentally and physically, and knowing that I had that desire in me to keep going.
"When you do something from when you're four years old, it's just on automatic pilot. You're young, you're bound to improve because you're learning. You're learning from experience, learning from matches. So when you're kind of at a standstill and you have to start from scratch, that's when you really test your motivation levels and that determination."
Given Sharapova's fame and fortune, some players might have been tempted by now to opt for an easier life. With estimated annual earnings of $25m (about £16m), the Russian is the world's highest-paid sportswoman. She had only Roger Federer and Rafael Nadal ahead of her in the most recent Forbes magazine list of the world's best-paid tennis players.
Her celebrity, moreover, is no longer dependent on success on the court. At the end of 2010 Sharapova signed an eight-year extension, said to be worth $70m (£45m), of her agreement with Nike, which is the biggest individual sponsorship deal in the history of women's sport. She has a collection of sportswear and is the face of Cole Haan, a Nike subsidiary which sells clothes, shoes, handbags and accessories. She takes a hands-on approach both to the commercial side of the business and to the designs that carry her name.
Sharapova, who says she still feels "like a teenager", has also found happiness off the court, having become engaged to the former Los Angeles Lakers basketballer, Sasha Vujacic. He now plays for a team in Istanbul, where they have a flat and lead what she calls "a very normal life" away from sport.
"I choose to be normal and I choose to have simplicity and enjoy simplicity in life," Sharapova said. "To me, the first days at home are always the best of my year, because after travelling and being on the road, where everything is taken care of and you're driven around and you're going to restaurants, it's nice to have that realistic feel about life. To have someone that you can share it with obviously makes it even better." She is sure that being happy in her private life has had a positive influence on her playing career. "I think it actually settles you in a way, because you know what you have in life, and you know a tennis career can only go on for so long."
She added: "We know our bodies are not going to allow us to keep doing our jobs after a certain age. So we're very content in that we know that when we are done with our crazy hectic lifestyles and our travels and our sports, we're going to have so much time together."
Not that Sharapova will be rushing into retirement. "Whenever that day comes, there is absolutely no doubt I will miss what I have done since I was four years old," she said. "I think the biggest thing is the competition. Why I play the sport is because of that competitive feeling. I don't think anything else in life gives me that and that's one of the reasons why I wanted to come back so quickly – and quicker than anyone else said I would.
"I love competing and there's nothing else in my life that gives me that, whether it's designing or doing a photo shoot. Many things in life are controlled by other people, especially in their work. In my work, in my career, everything is controlled in my hands.
"That gives me such a freedom in a way, because I know that if I lose a match it was in my hands. I could have won it, but I lost it. There are people around you in the team who help you and prepare you and get you ready, but at the end of the day it's about you, and it's you trying to beat your opponent. That's the best feeling."
Pain years: record since 2008 Australian title
French Open 4th round (lost to Dinara Safina)
Wimbledon 2nd round (lost to Alla Kudryavtseva)
US Open Did not compete
Australian Open Did not compete
French Open Quarter-finals (lost to Dominika Cibulkova)
Wimbledon 2nd round (lost to Gisela Dulko)
US Open 3rd rnd (lost to Mel Oudin)
Australian Open 1st round (lost to Maria Kirilenko)
French Open 3rd round (lost to Justine Henin)
Wimbledon 4th round (lost to Serena Williams)
US Open 4th rnd (lost to Caroline Wozniacki)
Australian Open 4th round (lost to Andrea Petkovic)
French Open Semi-final (lost to Li Na)
Wimbledon Final (lost to Petra Kvitova)
US Open 3rd rnd (l to Flavia Pennetta)
Grand Slam titles (3)
2004 Wimbledon; 2006 US Open;2008 Australian Open.