And besides, since this kicked off, I believe the current thinking is that going through pubity with testosterone gives lifelong athletic advantages.
Everyone goes through puberty with testosterone. It's what causes the changes in your body then, and what defines your initial sexual development in the womb.
Last I heard, Sememya has a form of androgen insensitivity syndrome, meaning that no matter how much testosterone her body produces, her system doesn't respond to it, which is what's caused her sexual development disorder resulting in the 'externally female appearance' that other female athletes have confirmed (those who'd seen her in the locker room have said she looks very definitely female, though not especially feminine). This insensitivity also means that any level of testosterone would not be an advantage for her as it doesn't impact her performance, precisely because her body doesn't respond to it. The high levels are effectively just a waste product, similar to other conditions like PCOS.
There's also an argument that testosterone itself isn't as much of a factor as previously asserted - Female body builders mostly shy away from testosterone, out of fear that they'll develop balls and facial hair or similar. However those women, who don't take testosterone and have a natural level around 1/10th of their male counterparts, are still able to achieve 85% the same level of muscle build as a male.
Caster is a Male with a particular Congenital Disorder of Sexual Development that only affects males and has fathered two children (via Artificial Insemination) with his wife.
Has the sperm donor actually been confirmed as Semenya?
I did have a quick look but there was no such information at the time, just news that they'd got two kids through IVF.
AIUI, her condition is that genetically she was supposed to develop as male, but didn't. Everyone starts as basically female and testosterone then drives the changes toward one or the other. In Semenya's case, the changes stalled and she ended up being born mostly female.