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 picked up English at 14, when my brain was still squishy and capable of learning.

It took me about 4 months before I felt comfortable having a full casual/social conversation and I was able to read a book and really understand what was being said. After 1 year, I started getting told that I had lost my accent altogether.

How? I spoke only english at home, only english at school, only english with my friends and I mostly played games with Americans on Ventrilo and TeamSpeak so I was forced to constantly think in english and put words into sentences.

Complete and total immersion.