Have you ever heard someone describe a person as “smart for their age”? Or maybe you’ve heard that interesting fact that girls’ brains are years more mature than boys during puberty? At the root of both of these sentiments is this idea of developmental age being one thing and chronological age another.
It may seem unusual to think that these ages don’t always match up throughout our lives, but it’s useful to keep both numbers in mind—especially in relation to one another—to make sure someone’s growth is on track and that they have the proper support that they need to thrive.
So let’s take a closer look at developmental age vs. chronological age, examining what each is and why they’re both important.
The Definition of Developmental Age
Developmental age refers to a person’s physical and/or mental development in respect to an age unit, as in the age at which a majority of people have achieved that milestone. For example, the CDC specifies that at 1 year old, most children walk while holding onto furniture while at five years old, most kids can count to 10.
Developmental age can be used to measure a child’s development across a range of categories, including verbal, emotional, and motor skills. So, a child could be five years old but have the language skills of a three or four-year-old if they’re unable to meet benchmarks for their age range—like describing objects or understanding rhyming.
Importance of Developmental Age
It’s particularly helpful for parents to keep in mind developmental age so that they can track whether a child is advancing as expected in terms of their physical and mental wellbeing. Sometimes developmental delays sort themselves on their own and a child “catches up” so to speak. Other times, they may need additional assistance to progress, or it could be a sign of a medical condition that needs attention.
Determining Developmental Age
To determine a child’s developmental age, you would need to assess their skills against the various age benchmarks. You can find a variety of different resources on the internet for this kind of monitoring. For example, the CDC offers a milestones checklist that you can refer to, and the non-profit Pathways.org also has its own downloadable checklists.
If you’re not comfortable determining someone’s developmental age on your own, it’s a good idea to speak with a doctor or specialist in that specific area of concern in order to get their professional assessment.
The Definition of Chronological Age
Chronological age is the standard we think of when we think of age and what we answer when someone asks, “How old are you?”. It’s the measurement of how much time has passed since someone’s birth to the present. For example, if someone was born in 1958 then their chronological age would be 65 in the year 2023.
Normally chronological age is given solely in years, as in “27 years old.” But, if you want to get super specific with it, you can also figure out how old you are down to the month, week, and day. With chronological age in mind, you’ll know not only how many candles to put on someone’s birthday cake, but also what age to check against with developmental age.
How to Calculate Chronological Age
You may have your age cemented in your memory as you prepare for your birthday party every year, but what if you want to calculate someone else’s chronological age? One way would be to take the current year and subtract the year they were born. Someone who was born in 1972 would be 51 years old in 2023 (2023 minus 1972 is 51).
If you want to calculate someone’s exact chronological age, meaning down to the number of days, that’s a bit harder to do with just some mental math. Instead, you can use a chronological age calculator by inputting the date of birth as well as what exact date you want to calculate their age on. This calculator will give you the age in years, months, weeks, and days.
Age Calculation in South Korea
Up until the end of 2022, South Korea used a traditional age system in which people were declared to be one year old at birth (rather than zero upon birth) and then added a year every first of January. This means that a baby who was born in December 2022 would be considered 2 years old in January 2023 according to the traditional Korean system.
Now that the laws have changed to match the widely accepted international system, South Koreans will identify as being one or two years younger than before!
Coming of Age
As you can see, there can be quite a difference in developmental age vs. chronological age. As you calculate chronological age and check it against developmental age benchmarks, you can follow someone’s growth and make sure they’re hitting all the right milestones at the right time. Besides that, knowing your exact chronological age can be a fun way to surprise someone. Next time a person asks how old you are, see if you can tell them that you’re X years, X months, and X days old!
Cindy is a freelance writer and editor with previous experience in marketing as well as book publishing. Along with her content writing for a diverse portfolio of clients, Cindy’s work has been featured in Thrillist, The Points Guy, Forbes, and more.