Math Riddle Involving Birthdays

Question

So someone asked me the following riddle:

If a girl is born in the 19th century, and on her first birthday she is 8. How is this possible? I think it's a simple mathematics problem but I can't find a way to figure it out.

Answer 1

If she was born on February 29, 1896, then the next time February 29 came around was in 1904 (due to the 100-year rule of the Gregorian Calendar, 1900 was not a leap year). That is, on her first "birthday", she was 8 years old.

(Cue Pirates of Penzance)