[@Gareth] Guardians will be around 10-19 like the Elemental Chosen Ones. 

They won't know they are 'Guardians' until they are told or learn of the prophecy. All they will know is they have powers while everyone won't.

Guardians can live wherever they want. When the time comes to protect the Chosen Ones, they will all meet.

The guardians will most likely be strangers to each other.