Katelyn,
I thoroughly understand where you are. In fact, it was a few years ago that I was in the exact same position.
I have the same past as you and it was until my late discovery of hormones and people who have done the change that I realized that I too could complete my wish to be female.
So yes, for me, it is a choice. I lived a long time as a male, and did reasonably well (except in relationships), so once I made my discovery of the possibility of change... I made the choice to change.
I think people get confused when other trans people talk about not having a choice: transition or die... The fault lies in how the word choice is used.
If you decide to commit suicide or to transition, it's still a choice. Whatever we do or don't do is a choice. You can choose to live life as an unhappy male, or you can choose to alter your body to fit your mind.
Now if you are presented with two options: suicide or transition, most people would choose the latter and feel that it's not really a choice but a matter of self preservation. You can CHOOSE to hold your breath or you can choose to breathe, but realistically, to stay alive, you'd want to breathe.
My opinion is that some people make it out to be that they are naturally the opposite sex, and that others, like you, and perhaps me, choose to change. You can pretty much ignore that and just go by what you feel.
You'll know when you're ready (or never ready) to be female, male or andro. When the feeling comes, you'll know it, then you don't have a choice because you've made it and there's only the mechanics of going through the process to change.
in the end, it is a choice TO make the change, however, if you're female in mind and spirit, then it's not really a choice because, for your completeness, you'll want the body to match.