Sarah, you really do make a great point here. Wait until a full adult life has been established, then basically crumble it. (providing there was not any serious foreknowledge of this happening) How much will likely have to change along with the legal and physical gender. At a much younger age, without all of that which has been established, the transition would go so much easier (I didn't say easy) without so much of a life that has to be dismantled.
But then what if *OOPS* transition really wasn't the correct choice, maybe living more of a dual gender existence.... It seems that the only way to really know you cannot live the life of the gender you are born with is to go through hell trying to live it for a long period of time, suffering most or all of it.