As a newbie, on my first post I was advised to research about Bitcoin in order to make some quality posts.
I made some efforts and I am now confused, that is why I created this topic.

1. I understood that there is a limited supply of BTC at 21million minable.
2. As at 2021 that about 18million BTC has already been mined.
3. And it is estimated that the last BTC would be mined at about 120yrs from now.

Now my confusion.
What mathematical analysis proves that BTC created by 2009 with a fixed supply of 21million. From 2009 to 2021 is about 12years, then about 18million has already been mined.
Now, the remaining which is about 2million+ will take about 120years to be mined?
I need clarification please.