Hi Chris, welcome!
I'm an electrician, not a doctor so don't take this as gospel... but I have been reading anything I can get my hands on over the past 55 years in hopes of finding something that will make me the woman I feel I should have been. No, I never found anything.
That being said, what I have learned over the years is the human body has growth plates that allow us to grow. Once they have fused, that's it, no more growth. Typically the human body continues some level of growth up to the age of 25. From what I've read, after that we begin to shrink but it's not normally noticeable until the later years.
Something I have also noticed is the human body can grow things through outside intervention, such as hormones, but it cannot shrink the same things to the same level. So if you go on T, your boobs may shrink but they won't disappear. If a MTF goes on E, the beard may slow growth but won't disappear. So it's grow, yes; shrink, probably not.
Soft tissues are the most dramatically affected for growth but not as much for "shrinkage". Once you've stopped growing don't count on your bone structure to change much except to make you shorter as you grow older.
Rule of thumb, if it's bony mass you want to change, the younger the better. But that is true for the entire body. It's just that bones don't change nearly as much as soft tissue.
