Age ain't nuthin but a number baby.
I'm 37 years old and rockin' it.
I don't think the difference from mid 20s to early to late 30s is all that big, probably not even early 40s either. Puberty is done, bone growth is done and hormone levels have more or less stabilized. What is left is the genetic lottery.
Teens and very early 20s for sure as you are still growing but even some people who start at say 18 can have passing problems.
I have more breast growth than some younger trans women, for example, even those who are dosed higher than me. It comes down to my genes, especially my mom and her family.
Really, genetics is what matters the most.