Hey look a sixth dude, welcome 8D

Most probably classical fantasy. What I was thinking is that mages draw from the vitality of beings around them (or themselves, if they're feeling suicidal). They don't necessarily have to draw out enough to kill the aforementioned living being, and someone schooled in magic can resist this, which is why mages tend to draw from plants and so forth. Because this can prove to be impractical, they'll often prepare vitality-imbued artifacts prior to battle. I suppose that, in a pinch, they can draw from themselves, but in doing this they risk killing themselves (hence suicidal). 

Magical talent tends to be, well, talent, and as such some individuals are more capable than others. It is possible for an individual that lacks talent to become capable through hard work, but it is rare. There's a knack to sensing life force you have to get before you can actually cast things. The Hand is the branch that focuses on magic, and if you're keen on learning more, you should go there, but all branches teach it to some degree. 

I hope this answers your question.