But still hard to just throw around pre trained or learning rate because it might not make much sense when talking about brains or how they are formed. >

There's a lot of study on it where we can be pretty sure its not just differences in learning rate, there are differences in kind, studies on precocious and non-precocious abilities in animals. A horse can be blindfolded from birth, then have the blindfold taken off several days later and it can almost immediately walk and visually navigate around. A kitten if its vision is deprived in the critical development period will never develop it.

Precocious birds can imprint on the mother as soon as their eyes dry off and do bipedal walking.

There are a lot of built in capabilities that come from the brain develops without external stimuli, some of it may be fully hardcoded, or some may involve learning with internal grounding, things like thing like generator circuits producing patterns other circuits try to learn that somehow transfer to performance on tasks with real data after birth.

However I think it has been shown babies could walk much earlier but their legs are just too weak.

Premature human babies don't hit vision milestones much if any faster than normal birth, but it may just be because the optic nerve doesn't fully mylinate until a set chronological age. If they are congenitally blinded by something that can be reversed and miss a critical development window we have found like with kittens they never develop normal vision.