Transgender bodies are different bodies. Different because they are imprinted with cross sex hormones/surgeries designed to reconfigure the natural body. Trans bodies are recognized as transgender (their actual sex) by these differences as much as or in many cases more than they are unrecognized by them. One of these recognizable differences in trans females is the forehead. While there are distinct differences (bone/cellular) in male and female foreheads, none adequately explain the trans female forehead, post hormone. These distinguishable forehead changes seem to occur somewhere around the 9 month period on testosterone, taking into account genetics and lifestyle.
The female face ages something like this:
This is an image of four random trans female foreheads, all four in their late teens/early twenties:
I've tried to explain away (to myself) varying possible factors as to why a young (healthy) female forehead (even on testosterone) would in a matter of months resemble that of a male forehead in his 70's or 80's. But no matter which way I turned, I failed. As there are little studies on the effects of testosterone on/in the female body and none on testosterone/the female body and aging, this observation stands alone in its speculation, (in HIGH doses testosterone accelerates aging in the female body) but in no way does its unicity invalidate it.