Saying he should be 14 years old means he has finished 13 years and started 14, or he has finished 14 and started 15?
for the international tournament minimum age is born 14 years before July 1st in the year of the competition. So 14 complete years of age as of July 1st is the cutoff.
(see RoboCupJunior General Rules – RoboCupJunior).
Example: Birthdate July 1st 2010 and earlier would be old enough for RCJ 2024, participants any younger than that are not eligible for participation in the worldwide tournament.
Please check with tournament organizers in your Region for their age limits - not all Regions implement the same minimum age. Lists of Regional representatives are available here: Community – RoboCupJunior
Hope it helps, if you have further questions just ask.