I do think their muscle would still be significantly reduced by the hormones, but the older someone is the more their body is “set in place.” This means any changes will take longer to occur and they may not happen to the degree that they would have if they started younger. So someone starting mid 20s - 30s likely won’t have skeletal changes, since that part of their body has already finished growing. (Someone starting as a young teen definitely will have skeletal changes though.)
As a young person who grew up on the internet, with no parental oversight, I can say it’s because there is a lot of right wing bullshit online that media companies love to push on their users. When I was a tween I got suckered into it hard when one day youtube decided to put mgtow videos in my recommended feed. I never initially searched for them. I did eventually get out of it, and I’m not entirely sure how, but I remember as a 13yo seeing trump in 2016 bully that disabled reporter and it really put a sour taste in my mouth. And then over the next few years that led to me leaving catholicism, becoming a socialist, and realizing I’m transgender and very gay.
With me being transgender and pan, that adds another aspect to it, because I think I knew subconsciously that I was queer as a tween, but growing up in an environment where I was repeatedly told those things were wrong led to me feeling absolutely miserable about myself, and misery loves company. And this also makes me wonder how many nazis are queer and don’t even realize it or refuse to recognize it.