I dont think you need a c cup to feel feminine, I see it a lot as a standard writing here by trans women, I am probably not getting a c cup, my mom as a d cup but she had children, and your boobs grow when you are pregnant, and my sister who is 2 years older than be has a 32b i think, so I will probably get there, on ther other hand all the girls in my family have wide hips, so maybe I will get luckier there.
Usually it's just genetics but it also takes a long time!
And for people that don't want foreign object or substance in their body like me, I heard some people get their own fat injected in the boobs too, so maybe that's an option for someone to look at. I am not sure how it works or about the results tho...