Dealing with Ancient Characters

I love getting under the skin of a character for the first time, seeing how they think, how they react, what private thoughts they have, even where they are ticklish. I know Fantasy is meant to be about huge magical explosions, dark, mysterious thoughts, and rooms lit only with candle light and strange blue auras, but actually, I am far more interested in how the people wrapped up in the world think when they cut their finger, go for a piss, see a girl/boy/dragon that they fancy, or celebrate the big five-oh-oh!