I remember a lot of what happened in elementary school. There was one particular person, a few years older than I was, who rode same bus I did. I could never figure out what gender they were, and that bothered me. It also intrigued me. I don't remember the face of any other kids on that bus as clearly as I remember the face of that person whose gender I still don't know.
From my own perspective, I was an odd kid the first few years of elementary school. I was assertive to the point of aggression with other kids, and I chased boys around the playground until they were all terrified of me. You probably would have called me a tomboy. By fifth grade, I had transitioned into a budding academic -- I focused more on schoolwork than other people, and I stayed that way for years. (It was adaptive.)
Growing up, I never thought of myself as a girl, or particularly liked "girl" stuff. My parents supported me in delving into those things that actually interested me, not in the things they thought I was supposed to be interested in because of my gender or my sex. Because of that support, the gender binary never felt terribly restrictive (or binary) to me. And it's only been in the last few years that I've really become aware of how the gender binary affects people -- and how many alternatives there are for breaking out of it, and how many people never fit in it to begin with.
I'll just talk about a couple of alternatives to the gender binary here, and then invite you to share your experience of gender at the end of the entry. I should say that gender is a category separate from (if often related to) biological sex, or genitalia; gender is a social and cultural construction, not than a physical fact.
Agender -- this is what I identify as! Essentially, people of any biological sex can identify this way. There's no surgery, no standardization, just a feeling that you don't fit in a "girl" box or a "boy" box. Being agender doesn't mean that you look a particular way or wear specific clothes. It means that my love of trucks as a kid is just as acceptable as a love of dolls would have been. It means that I can be exactly who I am, no matter who other people think I should be. It's a position that rejects the gender binary just by existing.
Transgender -- you don't identify as the gender that corresponds with the biological sex you were born with. Often, people use the term transgender interchangeably with the process of transitioning from one gender to another, but once you've transitioned, you (generally) identify as either male or female. The opposite of transgender is cisgender, where there is no disconnect between your physical sex and how you're comfortable expressing your gender. The myths about transgender people are persistent and damaging. The truth is that transpeople are far more likely to be the victims of sexual violence than cispeople are. Transpeople are slowly becoming more familiar to mainstream culture, but in the meantime, most people still haven't mastered basic courtesies -- things as simple as calling transpeople by the pronouns they choose.
Intersex -- is complicated! The term intersex covers a wide variety of reproductive or sexual characteristics that are not distinguishably male or female. Those characteristics can be anything from ambiguous genitalia, chromosomes that don't match a person's apparent sex, a mix of ovarian and testicular tissue... and people who are intersex may present as any gender, or as none.
This is by no means an exhaustive list of gender identities that offer alternatives to the male/female gender binary, but it's a place to start. I'll never know the gender of that person who rode the bus with me in elementary school. At least now I know enough to ask someone what gender they identify as, respect what they tell me, and not treat gender as the most important character trait a person can have.
Our culture has had a lot of boundaries knocked down in recent years, and we're just starting to question what the labels we choose really mean to each of us, and for our lives. So tell me, what does gender mean to you? How do you experience it? Does gender determine who you're attracted to, or who you feel safe around? Does gender restrict the clothing you feel comfortable wearing? Have you thought about what gender you identify as, or are you comfortable enough with the way people perceive you and interact with you that you never felt you had to struggle against those perceptions?