For example we refer to infants over a year as 13 months, 16 months, 24 months, etc. Is there a reason for this convention?
In: Biology
We use months to refer to their age because that is how we measure their developmental milestones. Babies develop really quickly, although most of the developments are quite subtle.
For example, a baby at 9 months old should be able to stand WITH assistance. They can put themself in a sitting position, or sit without support. A baby at 18 months should be able to walk independently, or even jump.
If a baby cannot meet their expected milestones by the time they reach a certain month, we must try to figure out what is causing this delay.
If I remember correctly, infants grow at a far faster rate in their first two years than afterwards.
So a baby from each month to month can still be quite a notable difference. After that, the grows slows down, and so it becomes less meaningful to track changes per month and the changes per year becomes more noticeable.
Because there’s such a large amount of development at such a young age. There can be a huge difference in a child of 1 and a child of 23 months. The former may not even be able to stand yet and the latter can be running around and holding a conversation with you.
Development under 2 years goes fast
You need that fidelity to show what point of development the child is at. Child goes from not being able to move, to flipping themselves, to crawling, to walking.
A 2 month old vs an 8th month old is like the difference between a 20 year old and a 30 year old in development. This rapid development continues until around 2.
Because they’re developing so fast that it’s still very helpful to break their age down by month. Once they get older, the rate of change shows down, so it’s more practical to just describe their age in years.
Thank you for all of your quick and thorough answers, it makes sense now you’ve laid it all out
When using years as a unit of time there is a level of approximation involved. So saying that they are 1 year old – they are somewhere between like 9 and 15 months. But if you use months, a 12 month old would be somewhere between 51 and 53 weeks.
When you are young you develop fast, so accurate time matters.
Because a month is a much more significant amount of time and their life when they are that young. A few months means the difference between a lot of physical and other milestones, being able to do/understand things vs. not.
All of the answers so far are great, but there’s a simpler, non-biological way of looking at things.
When you have very little, every bit counts. When you have a lot, the smaller pieces aren’t so significant.
0.1 is one five hundredth of fifty, one fiftieth of five, but a tenth of one and one hundred percent of 0.1. When a twenty year old is a month older, they’re very slightly older. When a one month old is a month older, they’ve literally doubled their age. Turning one is a milestone, sure, but you’re still working with small numbers. The fractions are still a significant proportion of the whole.
Because there’s a huge difference between a baby that just turned one and a baby that’s about to turn two. An expanded scale gives you a better description of where they are in growth progression.
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