What determines a Junior. For example, if a Junior turns 18 years old on the year of competing he will be classed as under 18. If he turns 19 years in the year of competing he will be under 21 years and not under 18 years. See the Bodybuilding criteria for more details.
For South Africa we have a possible 3 age groups for Juniors. Under 18 years, Under 21 Years and Under 23 years. This might not be at every show and will depend on the volume of athlete attendances. Each division could even be split further by making a under 75kg and over 75kg. Again this is based on the previous year's attendance.