(EXAMPLE) She was born on February 29 1896 and since 1900 wasn’t a leap year (I’ll explain later).The next leap year was February 29 1904 witch makes her eight years old.
The reason that 1900 wasn’t a leap year is it wasn’t able to be divided by 400.Only centuries that could be divided by 400 (like 2,000) could be leap years.
The reason that she is only eight years old is because that the 29th is only every 4 years. But if you skip a leap year you’d be eight on your first birthday.