i'm actually in the middle of an RP story about this, though mine goes off the rails of the 'tradition' clan sibko thing.
Trueborn warriors are born as phenotypes; mechwarrior, aerospace, elemental; though I belive that a cadet can change between them if their original training does not suit them. I think it was Bjorn Jorgenson, the Ghost Bear Khan, was born an elemental, but ended up becoming an aerospace pilot.
They are then placed in a créche, like kindergarten, where they are taught to read and swim and all that good stuff. The teachers at this stage are probably warriors who were considered a little too 'soft' for active duty.
Sibkos vary from clan to clan, some have specialised, small groups of the same phenotype, 20 or so cadets, others have large, mixed phenotype sibkos that can be up to 100 cadets.
Warriors are trained from birth and mature faster than children from other castes.
If they are injured or found unsuitable, they are dropped from their sibko to a lower caste, mechwarriors and aerospace go to scientist or tech, elementals usually to labour caste. This keeps the cadets motivated, as they are constantly bombarded with the 'might makes right; the warrior caste is the epitome of clan society' doctrine.
Training is harsh, because the Clans only want the best of the best, nothing else will do. This often results in physical or mental damage.
Instructors are usually solhama, older warriors, retired from the front lines. They hate their jobs and they hate their cadets.
Not entirely sure of the age of their Trial of Position for warrior, I think it was 20. Most clans only allow 1 trial, exceptional cases may warrant a second trial; for example, Smoke Jaguar allowed 2nd trials of cadets when they started to run low on capable warriors.
Even after survivng training and their trial, they may not end up in a glorius front-line unit, they may end up as second-line garrison troops, tankers, foot troops or police; so there is a lot of drive to excel.