Answer by taking a quote from the following article:

Mao Asada (Qian Tian  Zhen Yang , Asada Mao, born September 25, 1990) is a former Japanese competitive figure skater. She is the 2010 Olympic silver medalist, a three-time World champion (2008, 2010, 2014), a three-time Four Continents champion (2008, 2010, 2013), and a four-time Grand Prix Final champion (2005-06, 2008-09, 2012-13, 2013-14). She is the only female figure skater who has landed three triple Axel jumps in one competition, which she achieved at the 2010 Winter Olympics.

Asada began the 2013-14 season at the Japan Open, performing to Rachmaninoff Piano Concerto No. 2. She won gold at her two Grand Prix assignments, the 2013 Skate America and the 2013 NHK Trophy. With her victory at Skate America, she became the first singles skater, male or female, to win all seven of the current events on the Grand Prix series. At NHK Trophy, she set personal best scores for the free skating and total score. She advanced to the 2013-14 Grand Prix of Figure Skating Final where she took her fourth Grand Prix Final title. With this victory, she became the first woman to complete two consecutive Grand Prix seasons undefeated. At all three Grand Prix events, she won by a margin of over ten points. In late December, Asada competed in the 2013-14 Japan Championships. She led after a strong short program, but only placed 3rd in the free skating, dropping to 3rd overall.  In the team event at the 2014 Winter Olympic Games, Asada skated the ladies' short program. She fell on the triple axel and placed third individually; team Japan finished fifth. In the ladies' singles event, she placed 16th in the short program after falling on her triple axel, underrotating a triple flip, and doubling a triple loop. She rebounded in the free skating, earning a personal best score of 142.71 making her the third woman to score above the 140 mark after Kim Yuna 2010 Olympics score and Yulia Lipnitskaya 2014 Olympics team event score. This placed her third in the free skating and sixth overall. Asada's free skating was the most technically difficult of all the ladies and the only one with a triple axel.  At the 2014 World Championships, she broke the world record for the short program by scoring 78.66, 0.16 points higher than the former record set by Yuna Kim at the 2010 Winter Olympics. Asada went on to score 138.03 in the free skating, winning her third world title with a total of 216.69, a personal best for her. With this victory, she became the third woman in the last 45 years (along with Michelle Kwan and Katarina Witt) and the tenth woman to have won three world championship titles.  After winning the World Championship title, Asada stated that there was a 50-50 chance she would continue her career. On 19 May 2014, Asada announced she intended to skip the next season. Asada said she was mentally and physically tired and wanted a chance to focus on other aspects of her life, including attending university.

At what age did Mao Asada start her training?