We don't have a primaly category at an international competition (as 2019 Sydney).
We have rescue simulation (former CoSpace) in the international competition, it's hold open age.
When you want to know the minimum age of participant in the international competition. You shoud check RoboCupJunior HP.
The minimum age for 2020 is a plan.
I can not guarantee. You may need to contact your regional representative closely as it may change.
When you want to know other competition (RCAP or Euro Open, regional competition, etc ), please comtact the organization committee of the competition.