Oddly(?) though, most parents of young children don't refer to a baby as being "zero years old." Rather, we break them down into smaller units: two days old, six weeks old, four months old.
It helps that change happens particularly fast at that age, so the difference between newborn and 6 months is worth mentioning. Later on the units go up again and we just say "I'm in my 30s" :P
On the other hand a computer/car/house can also be 10 years old but not 0.
True, a few weeks can mean a few milestones at that age. It's still wild to me how quickly babies/kids develop. Every week brings new abilities, experiences, and emotions that weren't there before.
Exactly. What we call "new" is the 0th year. It's the same when you start counting seconds. You say "ok counting starts now", then wait a second and say "one", then wait and say "two". Before you say "one", you don't say zero, but it's implied by you waiting a second after you or someone says "go". That's still 0-indexed.
