I started T approx 4 months after I first figured out I was trans. I had not even tried to live as male until that point, though I was always male identified I had no idea transition was possible, so played the girl role well.
A therapist will want a certain number of sessions with you to determine you are trans. If you truly are you have nothing to worry about. A good therapist knows what questions to ask.
Be yourself and don't worry.
Jay