Heard from a friend in China: the age calculation portion of the app to schedule a marriage certificate had a bug where they subtracted 22 (legal minimum age) from the year, which resulted in 2002-02-29 which doesn't exist. The app intends to compare this against the user's birth date. The error handling code assumes all errors are from the comparison. The app then rejected all marriage certificate appointments by complaining that the users are too young to marry legally.
Relevant question for driving, voting, marrying, drinking. I'd assume just the date is compared.
If you are born on 29th, on future 28th you are considered "too young", regardless whether a 29th exists or not. On future March 1st you are "old enough" again regardless.
If a 29th exists you are old enough already on that date. Drinking beer in Germany at 16, I guess in some countries at 20 could be relevant cases. For the more common minimum age of 18 for many things, the limit is reached always on March, 1st because a 29th cannot exist.
You can say Feb 29 + 365 days = Feb 28. (And Feb 29 + 730 days = Feb 27.)
---
EDIT:
Note that in the context of birthdays, people use "calendar years," not "unit of time which is ~1 revolution around the sun."
Birthdays aren't celebrated every X million seconds after the moment of birth.
They are celebrated the same day each calendar year -- notwithstanding the fuzzy concept of "same day" for incongruent calendar years. There's no singuar right answer, but that is the core question: "what is the same day next (calendar) year?"
When I wrote "+ 1 year" I meant year to represent 365 or 365.25 days, not "the same day next year.":
>>> from datetime import date, timedelta
>>> year = timedelta(days=365.25)
>>> date(2024, 2, 29) + year
datetime.date(2025, 2, 28)
You may have interpreted it as begging the question, but it was not my intent—though I admit my formulation was ambiguous.
> Note that in the context of birthdays, people use "calendar years," not "unit of time which is ~1 revolution around the sun."
You've never heard someone say they've celebrated another trip around the Sun? I literally have a photo from 2007 of my daughter in Montessori celebrating her birthday by holding a globe and walking around a candle representing the Sun. I think most people probably don't really think about whether it's a calendar year or astronomical year because for most people, they are usually equivalent and it doesn't matter.
But that's all beside the point. All I meant to point out is that I disagree that March is more logical. I don't think logic points us to one month or the other. You may feel March is more logical, but I don't accept your priors, so for me March is not more logical than February.
> Birthdays aren't celebrated every X million seconds after the moment of birth.
As a surprise for a friend of mine, I threw him a gigasecond party on the day he turned 1000 million seconds old. Yes he was surprised, and a good time was had by all.
Many people say: Happy turn around the sun! and 365 is not the length of a year is the length of some years so, who knows... I'm against time zones and pro 28 days months and a couple of free days :D
Take DOB + n * 365.25 and then pick whatever day that falls in? That way it shouldn’t drift overall.
Though, I guess it would imply that what day of the year people celebrate on, would be off by one day on leap years compared to what it is on other years?
Feb 28 is definitely too early, you haven't lived a whole year yet since your birthday. So March 1 it is. It's not your birthday but you can celebrate having made it another year.
Think of it this way: if Feb 29 didn't exist that year, it would have been March 1.
If we're being scientific I guess all of us should move our birthday up by 1 day on leap years, but that seems annoying and not sure anyone really cares enough to.
No we should move our birthday celebration up by 6 hours every year. But that would be only relevant if we were celebrating at the exact hour of our birth.
365 days is what people commonly think of as a year. So if you're born Feb 29th and celebrate your birthday one year later (whether you call that 365 or 365.25), you land on Feb 28th. Then again, folks born between Jan 1 and Feb 28th of a leap year celebrate their birthdays 366 days later by calendar days.
Anyway, I'm not sure there's any more or less logical date to use and Feb 29th babies seem to choose both about equally:
> “I love when people ask me, ‘Do you celebrate on Feb. 28 or March 1?’” said Raenell Dawn, a co-founder of Honor Society of Leap Year Day Babies. “I get to tell them, ‘Both, because I can.’ But I’m a February baby; I was not born in March.” An informal poll of the society’s members showed about a 50-50 split between the two dates, said Ms. Dawn, who is celebrating her “Sweeter 16” by turning 64 this year.
If you want to celebrate your birthday at the moment earth reaches the same spot around the sun as when you were born, then we’d all have the same issue - we’d have to celebrate it 6 hours later every year, reseting every 4 years.
February 29 is very much a new day… which simply doesn’t exist on non-leap years.
