When people meet one another for the first time how can their demographic e.g. age, gender, race?

By the force and conviction of your age, gender, and racial stereotypes. Weve all got them to some degree, its just a matter of what they might be and whether or not we act on them: eg, if your a racist, the specific qualities you attribute to that race and how you feel about those qualities will have a dramatic impact on how you interact with someone before you get to know them as a human being.

Demographics and body language are often ALL we have to go on when we first meet someone (regardless of whether or not this is a good or useful thing). That is, before we get to know them, of course.