February 29 The Leap Day

February 29, known as a leap day in the Gregorian calendar, is a date that occurs in most years that are evenly divisible by 4, such as 2004, 2008, 2012 and 2016. Years that are evenly divisible by 100 do not contain a leap day, with the exception of years that are evenly divisible by 400, which do contain a leap day; thus 1900 did not contain a leap day while 2000 did. Years containing a leap day are called leap years. February 29 is the 60th day of the Gregorian calendar in such a year, with 306 days remaining until the end of that year.

Although most years of the modern calendar have 365 days, a complete revolution around the sun takes approximately 365 days and 6 hours. Every four years, during which an extra 24 hours have accumulated, one extra day is added to keep the count coordinated with the sun's apparent position.

It is, however, slightly inaccurate to calculate an additional 6 hours each year. A better approximation, derived from the Alfonsine tables, is that the Earth makes a complete revolution around the sun in 365 days, 5 hours, 49 minutes, and 16 seconds. To compensate for the difference, an end-of-century year is not a leap year unless it is also exactly divisible by 400. This means that the years 1600 and 2000 were leap years, as will be 2400 and 2800, but the years 1700, 1800 and 1900 were not, nor will be 2100, 2200 and 2300.

Births

so how about the person who born on February 29 ? did they get old ? yes, they did. 

A person who is born on February 29 may be called a "leap-ling" or a "leap year baby". In non-leap years, some leap-lings celebrate their birthday on either February 28 or March 1, while others only observe birthdays on the authentic intercalary dates.

For legal purposes, their legal birthdays depend on how different laws count time intervals. In England and Wales, the legal birthday of a leapling is March 1 in common years. The same applies in Hong Kong as well (see Leap Years, above). In Taiwan (Republic of China) and in New Zealand, the legal birthday of a leapling is February 28 in common years. So in England and Wales or in Hong Kong, a person born on February 29, 1996 will have legally reached 18 years old on March 1, 2014; in Taiwan and in New Zealand he or she legally becomes 18 on February 28, 2014.

"If a period fixed by weeks, months, and years does not commence from the beginning of a week, month, or year, it ends with the ending of the day which proceeds the day of the last week, month, or year which corresponds to that on which it began to commence. But if there is no corresponding day in the last month, the period ends with the ending of the last day of the last month.''