2020 first year of decade? NOT!
Let go all the way back to year 0, oh yea, doesn't start with year 0, starts with year 1. That makes the first decade from year 1 to year 10, second decade from year 11 to year 20, and so on. Then the 1st century is from year 1 to year 100, second century is from year 101 to year 200.
So this century started with year 2001 and will end with year 2100 (reason it's called the 21st century), the first decade is from year 2001 to year 2010 this decade started in 2011 and finishes this year, 2020. New decade starts next year, 2021 and ends in 2030, then year 2031 to year 2040.
SEE HOW THAT WORKS
Learn how to count years correctly.
Rant Over