How does it only take a year or so to speak/understand our first language but it’s so much harder to acquire another language?

Question

Like, we have a frame of reference (first language), so why is it so hard to learn another language after that?

In: Other

Answer 1

I believe it is understood that in our early years we are developing very quickly, and during these years, we absorb new information a lot easier.

You can look up the tragic case of Genie, a little girl who was isolated by her parents when she was a child and eventually rescued when she was I believe 13 years old? Because of this isolation, Genie never developed even her first language very well as she had missed that crucial developmental window. And even with extensive care, her language understanding never truly caught up to what was expected of someone at her age (even at around the age of 30).

The details are vague, as I read about this case a long time ago, so please feel free to correct me on anything I got wrong.