Grannyactivist - for a trans person to apply to have their birth certificate changed, they must have lived in their preferred gender for two years. In respect of gender re-assignment surgery, there is usually a period prior to this referred to as social gender role transition, where they live in their preferred gender for a period of time. This is usually one or two years.
If you feel that you are a blend of male and female, you might say that you are non-binary, or if you feel you fluctuate between the two you might choose to say gender-fluid. If you don't identify as either, you could describe yourself as agender.