Shy Bi TGirl

because breasts are made mostly of fat, which is squishy and only partially influenced by muscle and skeletal attachments, they can be basically any size or shape, and they CHANGE more or less constantly throughout your life. they are sensitive to hormonal, environmental, body compositional and pressure-based influences. they will continue to change size and shape until you die. i have a mild collagen disorder which makes me stretchier than other people in some ways and my breasts will change shape visibly if i don't wear a bra for a day. some people's breasts are so dense they wouldnt move at all even if you kept them squished or pulled for many hours at a time. human fat and skin is SO malleable and variable and it's a big reason we're such an interesting-looking species.

this link is a little website with some pictures of SOME different shapes of breasts, and for as varied as it is, it's actually still very limited in scope. it's focused on helping people find bras that fit but you can ignore that part if you want and just get an idea of some different shapes boobs can be, in a non-porn and non-medical context. they can be even more shapes than this. this gallery is intentionally in b&w and has been contrast-balanced to make everyone about the same color but different breast shapes are strongly genetic and will pop up in different locales and lineages. your boobs will often resemble those of your relatives (but not always).

it takes a long time for breasts to reach their "adult" shape, and it happens closer to about age 25-27 for many people than 18-20. a lot of medical literature will repeat the claim that women are "physically mature" by the age of 15-18, and this just isn't really true. if you are on HRT, please keep in mind that the average cis woman can start experiencing hormonal puberty when she's 9-12, and major changes can keep occurring until she's 25 or older. I'm AFAB, and my boobs went through a final growth change when i was 27! and i started the first stages of puberty (way before my first period, which is called "menarche" [men-ARK-ee]) when i was about 9. that's not outside the bounds of normalcy at all, average age of first period is about 12.5 years, and puberty itself starts a few years before that.

some of the later Tanner stages are related to gravity as well as fat accumulation, and sometimes they require a certain period of time to "settle" the very high, pointy puberty breasts down into more adult breast shapes. this takes time. the timelines doctors give HRT patients about breast growth are really weird to me as someone who grew breasts myself. sometimes i see people on HRT get worried about their breast growth not being big enough or adult enough after only a couple years, when the average cis woman's breasts take much longer than that (remember: started age 9, finished age 27!!) to mature and settle, and i just want people to not worry too much. i post about this regularly because i want people to see it. I've heard from many trans women that their actual doctors told them that they would get most or all of their breast growth within 2-3 years. that's not true for everyone, possibly for most people.