i would say the sooner, the better. if you aren't completely sure yet, try baby steps. maybe by dressing in the female clothes you want to wear in private. or by trying to go out by yourself dressed the part. it's a good idea to do this, but you should be careful. it's best to try experimenting with your gender by going out of town. other than that, you need to develop a good backbone. i think it's important to have the confidence and be able to say "this is who i am, if it's not good enough for you, you're not good enough for me."