you pretty much answered your first question with your second.
legally age is different than birthdays. here is some wiki info that helps:
A person born on February 29 may be called a "
leapling" or a "
leaper"
[11]. In common years they usually celebrate their
birthdays on February 28 or March 1.
For legal purposes, legal birthdays depend on how local laws count time intervals. For example, in
Taiwan, in common years, the legal birthday of a leapling is February 28, so a Taiwanese leapling born on February 29, 1980, legally reaches 18 years old on February 28, 1998.
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 precedes 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.
[12]
In some situations, March 1 is used as the birthday in a non-leap year since it then is the day just after February 28.
Technically, a leapling will have fewer
birthdays than their age in years. This phenomenon is exploited when a person claims to be only a quarter of their actual age, by counting their leap-year birthdays only. In
Gilbert and Sullivan's 1879
comic opera The Pirates of Penzance, Frederic the pirate apprentice discovers that he is bound to serve the pirates until his 21st
birthday rather than until his 21st
year.
