A ninja fights for their land, true. They are warriors, protectors, and many other things, but only in war time can they really be considered soldiers.

A young ninja generally performs simple tasks around the village, rarely anything more dangerous than an escort mission. As long as the abilities and the will to use them exist, there will always be a need for ninja, and the skills are best taught at a young age, while the mind is still fresh - much as the other educational basics are.