On December 26 of 2012, the WTF Competition Rules were updated and now in Article 4, paragraph 1.5 states: Contestants at the age of at least 17 years old in the year the pertinent tournament is held (15-17 years old fo Junior Taekwondo Championships and 12-14 years old for Cadet Championships). Ages for Youth Olympic Games might be different depending on the decision of the IOC.
In this same article it stated before that contestants could participate only if they were 15 years old or more. But now two years have been added as the age limit for an athlete to participate as an adult.
This important point has already been well explained and pointed in the invitation of “2013 WTF World Taekwondo Championships Puebla“, which states that a contestant in order to participate in the Championships: Must be 17 years old or older. An athlete who was born in the year of 1996 or before is eligible to participation in the Championships.