Language development starts earlier than most people think. Babies babble with all the sounds the human vocal tract can make, but by 6 months they are only babbling with the sounds of the language in their household. Up to age 12 or so you can learn a second language accent-free, but at that age an important developmental milestone cements phonemes in place.
About 45 years ago I heard Chomsky speak on the idea that the human brain is wired to learn a grammar as much as a bird is wired for birdsong. So learning some grammar is innate, but the particulars are up to environment.
Source: 1/2 a century ago I was a bit of a developmental linguistics nerd. Disclaimer: But many memories have faded.
About 45 years ago I heard Chomsky speak on the idea that the human brain is wired to learn a grammar as much as a bird is wired for birdsong. So learning some grammar is innate, but the particulars are up to environment.
Source: 1/2 a century ago I was a bit of a developmental linguistics nerd. Disclaimer: But many memories have faded.