Some gender non-conforming people may identify as transgender, but others don't. An example could be a woman who prefers to wear men's clothing and wear her hair short with no make-up. She may identify as a butch lesbian or simply be a straight woman who prefers a masculine look over a more feminine one.
Sexual orientation is different than how one expresses their gender. For example, a woman who dresses masculine could be straight, lesbian, bisexual or asexual. Although stereotypes would have you believe otherwise, people who are gender non-conforming are not necessarily gay, lesbian or bisexual.
Some studies have found that children who don't conform to the gender of their born sex when growing up are at an increased risk of abuse and Post Traumatic Stress Disorder. Boys who painted their nails or wore dresses and young girls who wear boy's clothes and play with "boy" toys were subjected to peer rejection, harassment and physical and verbal abuse from their peers.
As more and more people buck society's norms of what men and women should look and act like, perhaps there will be more acceptance for gender non-conforming young people.
See also: Gender Queer.