@DrOct I think that's fair. A decade is any 10 years. I could say my wife and I have been married over two decades and it wouldn't matter when I started counting. But calendar decades start the count at year 1. We are in the 10th year of the 202nd decade of the Gregorian calendar.

The first recorded zero appeared in Mesopotamia around 3 B.C. The Mayans invented it independently circa 4 A.D. It was later devised in India in the mid-fifth century, spread to Cambodia near the end of the seventh century, and into China and the Islamic countries at the end of the eighth. Zero reached western Europe in the 12th century.

So perhaps we Westerners are still learning to understand the concept of mathematical zero and counting and I will now start my point of reference for decades at my birthday. I will celebrate the new decade in 2026.