Will you have to go back a year if you were born on a leap year?

No. The only effect of being born on "leap day", February 29th, is that the other years you celebrate your birthday on February 28th.

Unless, of course, your name is Frederic and you were apprenticed to the Pirate King until your 21st Birthday; THEN you're screwed. Until you fall in love with the daughter of the Major-General.