Well, who says Nepeta isn’t a DD or a DDD?  Bind or not, it’s up to you if you prefer one look over the other!  Obviously some 13-year-olds do have DD/DDD chests, so it certainly isn’t implausible.

((Edit: Just to interject as well, there was a headcanon on homestuckheadcanons a while ago that said something along the lines of troll breasts, since they don’t use them for raising wigglers, being fat packs for protection because the females of the species are the fighters. The bigger the breasts, the more padding you need because you fight/adventure a lot. It ended by saying that Nepeta is totally stacked. TONS of people adopted it as their own headcanon, so don’t be afraid!))