You start at zero but 1 is the 1st number because zero is always assumed.
I think this was discussed at the end of the millennium...
Pay attention to the open sky
"Now that's a real shame when folks be throwin' away a perfectly good white boy like that."
This is the last year of the decade. The next decade will be the 2010s, just like the 1910s, 1920s, 1930s...