You don't understand the notion of entire numbers in mathematics. When you are born you start your first year indeed but you are ZERO years OLD. Maybe you are the only person that was 1 year old when you were born but most of us were zero years old and it took us a full year of life to say we are 1 year old. This is basic mathematics and if you don't get this I'm not surprised you don't understand how the Gregorian calendar is flawed.

The calendar is faulty from a mathematical point of view. People use the DECIMAL system when speaking of the calendar which is why 2000 is the start of the new millennium and the decimal system is a mathematical notion. Most people are indeed non mathematicians but they have common sense.

I would have loved to speak to you during the year 2000 as according to you, you were still in the 90's during that year.

I don't think you realize you just made CrazyGamer point.  When you are born you are in your first year of life just as you said.  When you turn 1 you are in your second year of your life.  when you turn 100 you are in your 101st year of your life or in other words the second century of your life since by definition a century is 100 years.   

Not exactly. Traditional counting would state that the year 2000 is already part of the 2000s, but at the same time it is the last year of the 20th century. This whole debate only extends to the start and end of centuries. 

On another note, I don't know if people who defend the existence of the year zero have considered that its addition would generate a funny consequence: any event you can come up with would've actually took place one year before of what the traditional counting says. Thus, Columubs would've actually arrived to the Americas in 1491, World War II would've actually begun in 1938, your birthdate one year earlier and today it would 2017, not 2018. It's only natural when what we consider to be the year 1 now would need to be the year 0. 

There is nothing "mathematical" about your argument. The choice of starting at 0 or 1 is entirely arbitrary, just as it is when we index mathematical sets. Sometimes it is convenient to start with 0, sometimes with 1. 

The Gregorian calendar (which we still use today) starts with the year 1 A.D. 100 full years after the start of the year 1 A.D would be the start of the year 101 A.D. A century is defined as a period of 100 years, therefore the year 101 is the start of the 2nd century. You'd have to define the latest century as only a period of 99 years or redefine the word "century" to get  the year 1900 as in the 20th century. 

The 21st century started in the year 2001 if one strictly applies the Gregorian calendar. In common usage, people don't strictly apply the Gregorian calendar, and therefore go by the first two digits of the year. 

https://en.wikipedia.org/wiki/Century

"Although a century can mean any arbitrary period of 100 years, there are two viewpoints on the nature of standard centuries. One is based on strict construction while the other appeals to popular culture.

According to the strict construction of the Gregorian calendar, the 1st century AD began with the year 1 and ended with the year 100. The 2nd century started with the year 101, the 3rd with 201, etc. The n-th century started/will start on the year (100 × n) − 99 and ends in 100 × n.^[2] Because of this, a century will only include one year, the centennial year, that starts with the century's number (e.g. 1900 was the last year of the 19th century).

Popular culture aligns centuries with decades, by grouping years based on their shared digits. In this model, the 20th century runs from 1900 to 1999, inclusive. This is sometimes known as the odometer effect. The astronomical year numbering and ISO 8601 systems both contain a year zero, therefore centuries would begin in years ending in '00' and conclude with years ending in '99'.^[3]

In the late 1990s, there was a dispute to whether the 21st century would begin on January 1, 2000, or January 1, 2001. Most people considered the 1999-2000 celebrations to mark the start of the 21st century, with fewer people marking the 2000-2001 celebrations as the starting point."

Exactly. Glad to see mathematics are not entirely lost on everybody

About the woman who passed away, really sad, and crazy to know she experienced the whole huge transformation of Japan throughout the 20th century.

Lol dumb reply. 

It was almost one in the morning when I wrote this, so you should be surprised that it isn't more convoluted and messed up than it is :P.

Yes, which is why I said that there is a difference between how the calendar is made and the mathematical notion of counting years in a decimal way.

I clearly explained that there never was a year zero or even 1 because in those days people did NOT use that counting. No one said, Wow it's the year zero or Wow it's the year 1...

It's only much later that a calendar was made and it was decided then that the years began at year 1 which is mathematically speaking a MISTAKE. And if you add to that the fact that our calendar is faulty anyway since Jesus was most certainly not born in 1, therefore there is no good reason to consider the calendar from anything else than a mathematical point of view, which is why we even continue using the Gregorian calendar. We are in 2018 so that we mathematically know that the PS4 was released in 2013, in entire numbers that means 5 years ago.

Which is why I said at the beginning that it is both right and wrong to consider the person who was born in 1900 as born in the 19th century, right from the point of view of this faulty calendar and wrong from a decimal (mathematical) point of view. But since counting years is simply mathematics, then it stands to reason that the mathematical argument is the superior one, therefore someone born in the year 1900 is actually born in the 20th century.

Yes, counting years is purely mathematics, but you must have made a mistake in your statement to conclude that 1900 is in the 20th century. 

Let's say someone is born the 1st of July 1900, he's (approximately) born in the middle of the 1900th year, so he's born 1899.5 years after the "beginning", starting the 1st of January 1. Like you said a century is 100 years long so the 1st century start from 0 years after the beginning and last until 100 years after that point in time. Identically, the 19th century start 1800 years after the beginning point, and last until 1900 years after it. 

The mistake comes from the impression people have, that, starting with year 1, something is missing, but actually everything make sense, because at any point in time during the year 1 you're at 0,xxx years after the beginning point. And it's obvious that the existence of a 0th year make as much sense as dividing by zero.

Ps : excuse my approximated English