If you want to start an argument, just ask someone about years and zero. For example, the new millennium started on January 1, 2000. But only 1999 years passed since the calendar was set up, since no year called “zero” was established. Thus, in reality, the millennium and the 21st century really began on January 1, 2001—not on January 1, 2000. But don’t worry about your age: If you were born on July 5, 1980, by July 5, 2020, you would be 40. After all, when you were born, you start with “zero,” unlike the human-made calendar.