You may think you know how old you are. But I’m about to tell you that you’re wrong.
You’re wrong. There, see? I told you.
The reality is, there are a few different biological and cultural ways to measure how long you’ve been farting around on Earth.
Your Cultural Age
In the Western world, we celebrate our first birthday after we’ve been expelled from our mother’s womb for a whole year.
But other cultures have a different set of rules.
In East Asia, the traditional method of ageing is to turn one year old on the day you’re born. This actually makes good sense because the heartbeat, brain activity and cell respiration have all been going on in the womb for eight or so months. Why not round it up to a year?
But then it gets weird.
Your second birthday occurs at the the beginning of the next calendar year, regardless of how long it’s been since your first birthday.
In Korea, that’s the 1st of January. In China, the new year starts on the 4th or 5th of February. As each new year rolls in, everyone gets one year older as a collective.
In extreme cases (late December births) this means that by early January, you’re considered two years old in Korea, while you are actually still a newborn by Western standards.
Confused? Great! Here’s a September birthday to illustrate the difference:
Here’s another way to view it. Count one year of age for each calendar year you’ve been witness to, even if only for a few days or weeks. So if you’re born in 2001, you’re one. In 2002, you’re two. In 2016, you’re 16. The significance is placed on the communal perspective (the year) rather than the personal perspective (your date of birth).
In Korea, this is the official method of ageing. It was formally abandoned in Japan, China and Vietnam a while ago, however it’s still often used informally, especially among the elderly and in rural areas.
So depending on where you live in the world, you could describe yourself as being 1-2 years older (or younger) than you previously thought. This got me thinking: which system is a more accurate reflection of your true biological age?
Your Biological Age
We can all agree that our biological existence began long before we were born.
Though we still debate the exact moment that life begins, let’s say, for the sake of this particular argument, it’s the moment the heart begins to beat in the womb. That adds eight months to your biological age.
But can we go back even further than that?
How about the living sperm and egg cells that fused to form your first complete set of unique DNA?
Think about your conception. Not too graphically, mind.
Men produce sperm every day; about 1,500 every second, if you’re really specific. It then takes 74 days for them to mature into little swimmers with the ability to fertilise an egg.
So the winning sperm that created you adds another 2.5 months to your current age, during which time, half of you existed primarily inside your father’s testicles.
So between womb-time (9.5 months) and sperm-in-development time (2.5 months), we can add a full year to your biological age. Just how Koreans do.
How many extra months or years can we add by examining your mother’s eggs?
For a long time, scientists thought that females were born with a finite set of eggs in her ovaries. Some 7 million, to be not-very-precise. They die off inside the ovaries continually, so by the time girls reach puberty they have only 700,000 eggs, or 10%, remaining.
Think about that. The egg of your conception was produced inside your mother’s ovaries, when she herself was a foetus inside your grandmother’s womb.
That adds another 16-50 odd years to your biological age, depending on how old your mother was when you were born. This leap of yolky logic has accelerated my current age from 33 years to 64 years.
However, this may be a bit of a tease. Recent research has identified a new type of stem cell in the ovaries that suggests new eggs are formed throughout the reproductive years.
So the egg that made me could be 64 years old, or it may be considerably younger. Either way, it probably adds a few more years to my biological age.
But You Aren’t An Egg, You Egg
Good point. I’m not an egg – and I’m not a sperm. Those cells are long gone.
So perhaps, in biological terms, I’m only as old as the oldest cell in my body right now. Hold old is that?
You might have heard the popular claim that all of the cells in your body are replaced every 7-10 years. This would make you, at most, just 10 years old.
This has a hint of science to it, but is mostly a myth or a misunderstanding.
In fact, different cells regenerate at different rates. Certain cells in the blood, small intestine, stomach, cervix and lungs live for a matter of days. Much like the Indonesian corpse flower which blooms for only 36 hours between years of vegetative growth.
Blood cells and dragonflies also have something in common:
And then there’s fat cells and domestic rabbits:
And while neural stem cells in the hippocampus continue to generate new neurons throughout life, other brain cells are never replaced. When it comes to the billions of other nerve cells in your brain, you’re stuck with what you’re born with.
So this whole idea of cell regeneration does absolutely bugger all for taking any years off of our biological age.
Which leads me to my final point.
Your Age On Other Worlds
Call me frivolous, but I decided to calculate how old I’d be if I lived on the other planets in our solar system. After all, a year is defined by how long a planet takes to revolve around its sun. And I’m not going to think about the maths any more than that.
So if I lived on Jupiter, I wouldn’t be counting Earth years. That would be silly. I’d be counting Jupiter years, where 1 Jovian year equals 11.86 Earth years.
So, being 33 of your puny Earth years makes me:
In fact, in the seemingly unlikely event that I did live on Pluto, my next (first) birthday would be on Saturday 4th February, 2232. About 216 Earth years from now.