I don't fully understand the struggles of people who have gender identity questions, but I believe in respecting the basic humanity of everyone to discover and be who they are. Is that enough to be an advocate?
Being an advocate implies action. That action can mean big stuff like lobbying and marching in protests, but it can also mean saying something when a friend is being transphobic. As long as you're willing to be engaged in whatever way is appropriate for you, you're a trans advocate :)