Ayla, as for genetics; from what I have seen, other women in you family will play a big part and will provide a good idea for what your physical changes will look like. Is it 100%, no. What percentage it is? Who knows as there too many variables to consider. There may be some studies out there; somewhere…..
As for age, within the legal limits, the younger the better, and probably based on the genetics thing, and what HRT your endo has you on. In my thinking, you and your medical support folks will be the best gauges for what you should, or can, expect. That said, different medical folks will use different research and have different ways of looking and doing things.
Just the way life is I guess. Sometimes you roll the dice, and….. Michelle