@Duskiy: CassAhhDee and Lestat221 Are right. However, the further away from puberty you are, the harder it will be. Before and shortly after puberty, you can transition almost fully. Later on it will be more difficult, since your voice is already set on your biological gender and body hair and body proportions are, too.
There is lots of YouTube montages of transitions, mostly mtf. I reckon you know them already, but I can link you to some if you want, Lestat221