In WRO, there are the following age groups (valid for 2024):

Age group Age Years of birth
Elementary 8 to 12 years old 2012 to 2016
Junior 11 to 15 years old 2009 to 2013
Senior 14 to 19 years old 2005 to 2010
Starter (Starter Category only) 6 to 10 years old 2014 to 2018

The deciding factor is the year when a participant was born, not the age they happen to be on the date of the competition.