You do know how fast they grow cause you can just talk to them, if she talks like a toddler she's a toddler. You don't actually have any of the child-like inquisitiveness about the world that Malice does, you sort of already know what to do, in the prologue when you escape you are entirely self sufficient.Still not a human. You don't know how fast they grow (mentally). You're trying to reason that she didn't mature just because she had to ask questions about things. It's not like the dragon grew up knowing things that it didn't know either. It's obvious that one wouldn't know since they had no experience. Born wanting to fuck is instinctive, and doesn't mean Mental maturity.
To put it another way, what evidence is there that the dragon is a child at all? With Malice, you have plenty of moments where she's just a kid, but you never have any of those.
In the real world, a kitten in a year is already an adult cat. A human baby in a year is still a baby. So likewise, you mature the moment you leave your egg while Malice doesn't.