One of my cousins was born before a leap year. She's actually 14 years old.
I have a friend at school that was actually born on a leap year on February 29. She celebrates it February 28.
I don't know. My cousin is "officially" four years old this year (he's sixteen) because he was born on a leap year ;) ; I think his mother does it the day before, but I could be wrong.
I think I would celebrate it on both days!