I was born on 2004-02-25, but I will have lived for 21 years on 2025-02-24. I'm not special, this happens for everyone. This is because the calander year varies between 365 and 366 days, while an average greorian year is 365.2425 days. Fx, I was born 02-25 on a leap year, which means it was 366 days till it was 02-25 again. But I was born at 13:55, and 2004-02-25 13:55 + 365.2425 days ends up being 2005-02-24 18:44:42, so I had already lived for 1 average Gregorian year on 02-24.
Here's a calculator to enter your birthdatetime to see when you will be different ages:
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There are some patterns on smaller scales, as you likely can see, but the full period is 400 years (starting year 0 (yes that exists)).
In my lifetime (of around 85) I can expect to most birthdays on 24th, eventho I was born on the 25th.
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Timezones end up making birthdays even more confusing, if you define your birthday on local timezone, and you want to celebrate when you have lived for x amount of avg greorian years, then your birthday will be different in different parts of the world. Due to funky timezones, you can have 3 birthdays at same time? Baker and Howland Islands are UTC-12:00, and Kiribati' Lone Islands are UTC+14, if you have your birthday 10:00-11:59 UTC, you will have 3 birthdays!
Ages where the previously given birthday falls between 10:00-11:59 (meaning there will be 3 different dates):
Credit to Leaflet as well as mapshaper and timezone-boundary-builder.
A year is different lenght, either 365 or 366 days, this means it's not a unit of time, its a duoit of time. When someone tells you their age in years, you also need to know which year they were x years old, otherwise you dunno how many leap years they have lived through, and you don't know their exact age
This may seem all fun and stuff, and it is :) but there might also be some more serious implications.
Imo if u celebrate some1s birthday on their exact birthday its respectful, cuz you celebrate that they have been alive, not the day of the month they happened to have been born on.
But then again, it would be quite cumbersome to know someones birthdatetime, especially when they aren't very close to u. So maybe its for the best.
Many laws are defined by age (such as when you can vote, drink, or drive), but how does the law define age? I'm obviously not a lawyer, so maybe I'm just bad at this, but I can't find the legal definition of age in any country (and I'm too lazy to Google for more than 5 minutes).
Age is typically calculated by subtracting the year of birth from the current year and considering whether the person has already had their birthday that year. However, this depends on how birthdays are defined, and most people define birthdays as the same MM-DD of the year they were born, which, as previously shown, isn't the same as the actual time spent alive.
Since that age is based on "duoit years," it seems a bit unfair that not everyone has to wait the same amount of time until they can vote (potentially anti-democratic even). By "duoit years," I would've had to wait until 2022-02-25 before I could buy alcohol in my country, but I had already lived 18 average Gregorian years by 2022-02-24. I lost about an hour of time to buy alcohol—that's discrimination based on birth time, which isn't something I chose myself. I was born with it. It sounds like a human rights violation to treat people based on something they’re born with, rather than their personality.
But I don't really know how the law works, and I wasn't buying alcohol on 2022-02-24 at 23:00, so it didn't affect me. However, in some hypothetical scenario, it might affect someone, and it could have worse consequences.
A different scenario might involve prison time. If you get sentenced to prison for 1 year, is that based on "duoit" or "unit" years? Because it would be unfair if it was based on "duoit" years.