Yes, you have to draw the line somewhere.
If history is any guide, the last veteran dies about ~90 years after the war ends. So the last WW2 vet may die in the 2030s.
For me, the last WW2 vets and last people who were alive during the great depression will both be disappointing. That was a lot of history we will lose.
I think that’s where there’s some disagreement - my understanding, and certainly for most people I know whom I’ve asked, AD does begin with the year “zero” - much as the first patient to get a horrible disease is called “Patient Zero”, not “Patient One” and potentially serious but as yet unpatched hackable flaws in software are known as “Zero Day exploits”.
Fine, the last person who was born in a year that started with 18xx has just died.
It used to be common to say ‘In the Year of Our Lord…’ So the first year of Jesus’s life, he was in his first year. Thus, when Jesus was zero to one year old, he was in his first year and the first year was Year 1.
I agree with Martini about common usage for years included in century names, but Johnny L.A. is right about Year 1*. Upshot: the first century AD (and BC, too) had 99 years, while all other centuries have 100 years each.
*I’m reminded of music, where the interval of a “third” (say) is really a “distance” of two whole tones, because the scale starts at 1, not at 0.
That’s not a “disagreement,” that’s simply a mistake. AD does not include a year zero, never has, and never will.
The OP was wrong to say 19th Century, but the article linked by them says this:
…which is correct.
I emailed Cecil a million years ago (probably more like 18 years ago) to clarify when the new millennium started, 2000 or 2001. He, or someone representing him, responded that it starts whenever you want it to. Same for a century. Same even for a decade. For instance, he defined the 60’s as 1963 - 1972 or some such nonsense. I wish I could find that email. Anyway, if you want to say the 19th century was 1800 - 1899, you’re not wrong according to Cecil!
I think we should just decide as a society that the first century was 99 years long and ran from AD 1-99 and the ones that followed were 100 years long. 
We can fix this if we restart the numbering again. And this time, do it starting with year zero like any self-respecting numerate society would do.
So 0-99 is the 100 years of the zeroth Century. Then 100-199 is the first Century. etc. Don’t forget the 12 months are numbered zero through 11 and the 30 days are 0-29. Monday can still be the first day of the week since Sunday is the zeroth day. 
Now all we have to do is come up with a calamity so world-shaking as to make us want to renumber. :eek:
'The ‘60s’ is a cultural decade, rather than a ‘defined’ decade. Any ten year period is a decade. For example, ‘Jim-Bob, who is 50, is five decades old.’ A named decade or century that begins in the first year of that decade or century, starts at Year 1 and runs through Year 10 or Year 100, respectively. (And since it is a named century, ‘Century’ has a capital C.) There is no way around this, since we have defined ‘first’ as ‘one’, and we started counting from 1. Which makes sense. If someone asks you to count to 10, do you count ‘Zero, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10’? Most people don’t.
Right, good idea. Defining the 19th Century as 1800 - 1899 relies on either saying the first century had only 99 years, or that it was 0 - 99. If you count years from 0, you would naturally have to count centuries starting from 0 too.
I love the idea of asking people in a bar for their opinions. If I were omnipotent ruler of the world, and in a bad mood, I’d go to bars and ask people to find country X on a map. Then I’d go to that country and force all its inhabitants to move to the bar patrons’ consensus of where their country was.
This debate has always been a bit of a mind bender for me. Supposedly there’s no “year zero” but yet there is a “first year”. When a child is born, he is in a sense born in a “year zero” as that’s his “first year”. He’s not “one” until he’s “completed” one year of life (0-1).
A child is in his first year, or Year 1. When he has been out of the womb for one year, he is one year old. The second after the exact one-year anniversary of his birth, he is in his second year.
My grandfather told me this weekend that he wants to be one of the last surviving WWII vets and he may very well be. His own grandfather was one the last surviving Civil War vets and lasted until 1949 at just shy of 101 despite doing absolutely nothing to promote his own longevity except for a strict regime of whiskey, cigars and women. My grandfather is 92, still drives and runs his own real estate company. I wouldn’t be surprised at all if he makes it past 105 in 2030 to be one of the last WWII vets still standing.
The difference between ordinal and cardinal numbers is a standard part of US education. But like a lot of Math stuff, people flush it from their minds the day after the test.
So you are 2 years old in your 3rd year. This off-by-one property should be clear to one and all, but since “it’s just Math” not only are people allowed to immediately forget it but they are also allowed to make horrible arguments against the idea!
Exactly. As renowned FBI agent and Oxford-educated Ph.D. Fox Mulder once wisely said, when discussing precisely this issue of when new centuries start: “No one likes a math geek, Scully.” 
The impression is got, that people have been arguing about centuries’ limits, year zero, etc., since forever – with no consensus, and few folk convinced into changing their views. Comes to mind a passage from Solzhenitsyn’s The First Circle, in which 1949 is shortly to end, and 1950 to begin; and there’s a heated argument between prisoners in their (by Gulag standards, luxurious) scientific research facility, as to whether this transition marks the mid-point of the 20th century, or not – IIRC, “they kept getting hung up by the question of the exact year of Christ’s birth”.
You probably think an ounce of gold should be heavier than an ounce of steel too! 