Water Warriors, Fire Warriors and Ice Sages do not train to become their respective Caste until they reach the rank of Gurei Deshi. Wind Sages are the only caste the requires the student to begin training at Genin level. If you really want to begin training as a Water Warrior while a genin, that's perfectly fine, but it's not recommended. Once you pick a caste you cannot change your choice, especially in the case of Wind Sages. Water Warriors, Fire Warriors and Ice Sages can change their caste if they have enough time left to train and have council approval. Wind Sages, however, can never change their caste choice. It's all up to your master. If your Master is not a Water Warrior, it is discouraged from them teaching you in the ways of a Water Warrior. Kahn is a different matter, since he is not only a council member (and thus privy to all the secrets and philosophies of all the castes) but he is also taking advice from Me on how to train a Wind Sage. I'd offer to teach you the ways of a Water Warrior, since I"m essentially the only one qualified to teach any caste since I made them all, but I just don't have the time at the moment. If you cannot find a Water Warrior master and really want to learn the ways of that caste while you're a Genin, however, I can probably move some things around to accommodate you.