For most twentysomethings it is a landmark to be greeted with a sigh rather than a smile. For professional sportsmen and women it can be a sign that the end is much closer than the beginning. For Roger Federer it is a cause for celebration.
"I'm looking forward to turning 30," Federer says as he looks ahead to his birthday on Monday. "Birthdays happen. They're part of life. I'm happy I'm getting older. I'd rather be 30 than 20, to be honest. To me it's a nice time."
Thirteen years on the professional tour and 967 matches have earned Federer more than $63m (£38.5m) in prize-money and 67 titles, including a world record 16 at Grand Slam level, but the best player of all time is still hungry for success. Like the other leading men, he returns to competition at next week's Montreal Masters, with the US Open to follow three weeks later. "Every time the US Open rolls around I'm very, very excited," Federer said from his home in Switzerland as he prepared for the North American hard-court season.
Asked if this might be one of his last opportunities to add to his five US Open titles, Federer says: "I don't feel it's my last chance, not at all. I see many more chances to come. Maybe it's the last Grand Slam of the season, fine, but still there are many more tournaments than just Grand Slams. I know I'll be being measured very often just by my Grand Slam results, which is fortunate or unfortunate depending how you look at it. My game is in a good place right now."
Despite Federer's optimism, the statistics suggest he might struggle to add to his haul of major titles. Since the turn of the century Pete Sampras and Andre Agassi are the only men who have won Grand Slam singles tournaments in their thirties, the former having claimed the US Open at 31 in 2002 and the latter the last of his major crowns at the 2003 Australian Open when 32.
Federer, meanwhile, has not won a Grand Slam tournament since last year's Australian Open. All six subsequent major titles have been won by either Novak Djokovic or Rafael Nadal, who are six and five years younger respectively. Having spent 285 weeks at the top of the world rankings (a record bettered only by Sampras, who led for 286 weeks), Federer now trails a distant third behind the Serb and the Spaniard.
At one time there was a feeling that the 2012 Olympics at Wimbledon might be an appropriate moment for Federer to put his rackets away, but he insists he has no retirement plans. "I probably plan one and a half years ahead," he says. "I'm already thinking beyond the Olympics."
He adds: "I've always said that I find inspiration from guys who have played for a very long time, like Agassi, Jimmy Connors, Ken Rosewall, Rod Laver. It's very inspiring to see what they were able to do over a very long period of time."
Federer said he took heart from his season so far, despite having lost to Djokovic in the Australian Open semi-finals, to Nadal in the French Open final and to Jo-Wilfried Tsonga in the Wimbledon quarter-finals (a defeat he described as "unfortunate"). Federer says: "I don't feel I've walked off many matches this year feeling I played poorly."
He felt he was "really close to making something special happen" and adds: "I've won so much you feel like if you put yourself in the right position and do all the right things, you'll definitely get a shot again at winning any big tournaments, or any tournament for that matter."
Having taken a week off after helping Switzerland beat Portugal in the Davis Cup last month, Federer has been back on the practice court for nearly three weeks. "Physically I'm fine," he says. "This time around I didn't go through any aches and pains except muscle pain in the early stages when I started my practice again, but that's completely normal. Now I feel really eager to go.
"In the preparation, nothing changes. Do you listen to your body more? Yes, you do. Are you wiser? Yes, you are. Are you more experienced? Yes. Do you have a thousand matches in your body? Yes, you do. You just go with what you have. The important thing is I work hard, I'm professional and I enjoy my time on tour."
As for his forthcoming milestone, Federer says: "I'm excited to see how the Canadians are going to celebrate my birthday this time around. Sometimes they start singing 'Happy Birthday' during a match. I'm not going to play on Monday, but you never know if they're going to do something crazy another day."