[mmmmmbop]

> We do the same with people's ages.

No, we don't.

When we refer to 'the first year of life', we mean the time from birth until you turn 1.

Similarly, you'd say something like 'you're a child in the first decade of your life and slowly start to mature into a young adult by the end of the second decade', referring to 0-9 and 10-19, respectively.

[Uehreka]

> No, we don't.

But practically speaking we usually do. I always hear people refer to events in their life happening “when I was 26” and never “in the 27th year of my life”. Sure you could say the latter, but practically speaking people don’t (at least in English).

[mjmahone17]

“Half one” is archaic English, and common German, for 12:30. Similarly “my 27th year” just sounds archaic to me: I wonder if you went through a bunch of 19th century writing if you’d see ages more often be “Xth year” vs “X-1 years old”.

There may be something cultural that caused such a shift, like a change in how math or reading is taught (or even that it’s nearly universally taught, which changes how we think and speak because now a sizeable chunk of the population thinks in visually written words rather than sounds).

[xg15]

I think of the age number "practically" as the number of "birthday celebrations" I have experienced, excluding the actual day of birth. That's the same as the amount of completed years I've lived on this earth, and one less than the year I'm living in, because that year is not yet completed. (Except of course on birthdays)

But I think this also illustrates just how averse our culture is to using zero-indexing in counts: The age number absolutely is zero-indexed - a baby before before the first birthday is zero years old. But no one calls it like that, instead we drop the year count entirely and fall back to the next-largest nonzero unit, i.e. we say the baby is so-and-so-many months old. And for newborns not yet a month old, we count in weeks, etc.

I think, culturally, it's not that surprising as this method of counting is older than the entire concept of "zero". But I think it shows that there is little hope of convincing a large number of non-nerd people to start counting things with zeros.

[mtlmtlmtlmtl]

That's not really indexing from 0 though. It's just rounding the amount of time you've lived down to the nearest year. You get the same number, but semantically you're saying roughly how old you are, not which year you're in. This becomes obvious when you talk to small children, who tend to insist on saying e.g "I'm 4 and a half". And talking about children in their first year, no one says they're 0. They say they're n days/weeks/months old.

[SllX]

In an indirect manner, we do mark having lived the 27th year in the following forms, we just don’t say it exactly the way you phrased it:

1. On your 26th Birthday, when you say you turned 26 what it means is that you have now lived 26 years. People generally understand this, even if they are going to be spending the next year saying they are 26.

2. It is not uncommon for people to demarcate their age on their birthday in revolutions around the Sun, as a kind of meme. “I’ve now traveled around the Sun twenty-six times.” or something like that, when reflecting on their lives on their Birthday.

The colloquial usage is our legally-defined age. A shortcut for our laws to take, the age-gating ones anyway. It hasn’t replaced our cultural understanding of what the first year of our life actually was.

[jcelerier]

The first year of life is the year indexed with zero, just like the first centimeter/inch in a ruler is the centimeter/inch indexed with zero

[Sardtok]

And so is the first century of the zero-indexed calendar.

[mmmmmbop]

I agree, that was my point.

[kelnos]

> When we refer to 'the first year of life', we mean the time from birth until you turn 1.

Sure, but no one ever uses that phrasing after you turn one. Then it's just "when they were one", "when they were five", whatever.

So sure, maybe we can continue to say "the 1st century", but for dates 100 and later, no more.

[rootusrootus]

> Sure, but no one ever uses that phrasing after you turn one.

Heck, few people say anything about 'the first year of life' even when talking about someone that young. It is too imprecise, because things change so rapidly. In my experience the most common convention is to use months to describe age before someone turns 2.

[furyofantares]

On your sixth birthday we put a big 5 on your cake and call you a 5 year old all year.

Can't say I've ever had to refer to someone's first year or first decade of their life, but sure I'd do that if it came up. Meanwhile, 0-indexed age comes up all the time.

[subroutine]

The number we put on the cake represents the number of "years old" (i.e. the number of birthday anniversaries) not the number of birth days someone had (obviously). Zero year-olds are 0, one year-olds are 1, ...

[drdec]

> On your sixth birthday we put a big 5 on your cake and call you a 5 year old all year.

If you are going to be that pedantic, I would point out that one only has one birthday.

(Well, unless one's mother is extremely unlucky.)

[layer8]

birthday != date of birth

“Birthday” really means “anniversary of the date of birth”.

[daynthelife]

My preference is semi-compatible with both conventions:

First = 0 Second = 1 Toward = 2 Third = 3 …

This way, the semantic meaning of the words “first” (prior to all others) and “second” (prior to all but one) are preserved, but we get sensical indexing as well.