Or, why people think I do. Many other people do as well, probably because they intuit what I overthink.
Is someone 15, going on 16, or are they just 15? It can get annoying (and creepy…why am I talking about 15 year olds?), and I’ve heard plenty of people complain about people talking that way.
I say I’m 27, though I’m really 26. The day of birth is somewhat arbitrary as a day of celebration in my opinion, but I understand and accept it is helpful to establish a base from which to determine age. Is age truly relevant? Probably not, but we like to accept it as important. We need SOME standard of judging people by, and it’s too complex to judge on merit and ability, so why not age?
Anyway, 6 months after your birthday, any given individual nudges the line from closer-to-last-birthday to closer-to-next-birthday. So, just round to the nearest birthday. This way, you remain within 6 months error of what people are asking. If we do it the traditional way, then one day before your birthday, there are 364 days error in your communications.
Now go and lie more about your age.