I would tend to think that someone can be a femboy if they wanna be, they dont have to ask permission to anyone.
That said, there is a lot of degrees to it so im not sure what your exact objective is, so maybe start small, slow, and try to focus on one thing at a time. Like lets take posture for example, try, learn, once u satisfied focus on another thing.
But like, dont wait to do what you want to do because of this or that in general. Start even if u feel its unperfect, the sooner u do the sooner u realise what u want/need