Hi Riley,
How quickly or slowly we follow the path to authenticity is uniquely personal and individual. If your parents will support it, you can begin talking to a counselor and getting started now. The transition works better the younger you are from a strictly physical standpoint, but that ought not be your biggest motivator. How well you relate to yourself is so very important. Do you really understand what this path entails? That is I think what your parents concerns are. That is what mine would be if I were them. Getting as much input and professional guidance as you can first is my suggestion, and then with as much knowledge as you can collect, make your decision without regret or hesitation. Good Luck and Blessings,
Julie