Hell, animals are an even better example. Many animals pop out of the womb and start walking and eating and acting just like an adult!
That is only surprising because for simplicity age is counted from birth not from conception.
One could argue that humans are more adaptable to novel environments
If you wanna get philosophical then the decades of research that humans did is also AI "pre-training". And all of that is built on knowledge that humans have spent our whole existence amassing so maybe all of human "pre-training" is also AI pre-training.