I'm 20 and size 36D, sometimes 36DD
Every single time I need to buy a bra I look at it and think it's going to be way too big but then I put it on and it's fine. But I still think my boobs are smaller. Maybe because they went from B cup to D in like 2 years and I've assumed they stopped growing when I was 18. So I didn't really notice the gradual growth.