February 29th only comes around every 4 years, except for years ending in '00 unless divisible by 400 (2100, 2200, 2300, 2500, 2600, 2700, 2900, and 3000 will not be leap years). This is to keep our calendar straightened out. It has something to do with the amount of time that the earth rotates around the sun being different than the times it rotates on it's axis.? This is explained by the leap second.
Find out more about leap year here, and here.
Supposedly, a 1288 law by the Queen said if a marriage proposal was refused by the man there were fines. Because men felt that put them at too great a risk, the tradition was in some places tightened to restricting female proposals to the modern leap day, Feb.29th, or to the medieval leap day, Feb.25th, and that the women on the hunt were to wear breeches. A few hundred years later it was changed: "Women looking to take advantage of their opportunity to pitch woo were expected to wear a scarlet petticoat -- fair warning, if you will." After all, it was MUCH harder to get a divorce back then. I was too shy to do anything like that before I was married. I was even to shy to accept a date from Steve the first time he asked. He felt rejected, but decided to give it another try and I said okay to a movie date. I think it's more fun letting the guy do the wooing.
People born on February 29th may be called a "leapling" or "leaper". In common years they usually celebrate their birthdays on February 28th or March 1st.
There are many instances in children's literature where a person's claim to be only a quarter of their actual age turns out to be based on counting their leap-year birthdays. This confused reasoning is used in the plot of the 1879 comic opera, The Pirates of Penzance.