Age
Age isn't exactly a universally standardized variable. Some countries even have multiple types of ages such as China with Traditional Age, Modern Age, and Real Age.
Some count being born as having an age of 1. Some add another year on the first new years leading to an age difference of somewhere between 1 and 2 years. This is the case in South Korea, where they only celebrate birthdays on new years. Thus everyone's age can be calculated as Age = (Current Year − Birth Year) + 1. In essence, they count the number of calendar years you have witnessed.