[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.