For the title above "Why does it have to be a leap year?", I can provide you the anwser. But it doesn't seem to match what you're trying to say, nothing is related to that sentence "I'm turning 15 on March 1 can't wait so I can apply for staff" that you mentioned. Mkay, this is why it must be a leap year. During the time of BC (Before Christ), they've made this "Leap Day" on Febuary, it's because the planet that we live in (As well I might simplify this, called "Earth" lol) doesn't spin perfectly for 365 days, instead... it might spin for an additional time of 20.7 - 23.5 hours. But for us, we calculate it as rounded up 24 hours to make it a day. This includes in the Roman calandar and all other types of calandars such as Chinese calandar. EDIT: Once every 4 years, a leap year only occurs. It isn't every year's affair tho.
About Chinese calendar, we used to use lunar calendars (each month = 1 moon cycle) until the westernization in the 20th century (Now lunar calendars are used by farmers and generally elderly). In the lunar calendar, we add an extra month in the leap year instead of an extra day.
The belief of filipinos in leap year is the men are more prone to the (forgot the word ) of woman. It is possible that the woman will propose to the man and it is better not to be married in leap year or have a baby. @ZombieGirlSky Good thing there are'nt leap year on minecraft lol xD