I started at 65 and now have about the same figure as my sister except for the hips. (My shoulders may be marginally wider, too, but it isn't noticeable.)
I have read that there can be some skeletal changes until early-to-mid 20s, so 20 is not too old. But look around. Women come in great variety. Some are slim-hipped and some full-hipped. Some have broad shoulders and some have narrow shoulders. And so it goes.
And be sure to have a doctor's supervision. Hormone treatment can cause all sorts of problems you won't see until years later. I assume that you want to be a healthy, pretty woman, not a ruined shell.
- Kate