IIRC, it's the leap year issue. There are NOT leap year events in years that are evenly divisible by 100, UNLESS also divisible by 400.
Example: The child is born Feb 29th, 1896. Year 1900 is not a leap year, (as it's divisble by 100, but not 400) so Feb 29th does not come around. So the next occurence of Feb 29th would be 1904; hence he/she has marched 8 years towards the grave, with one birthday.
That would NOT apply to a kid born on Feb 29th, 1996, because the next leap year is not only divisible by 100, but ALSO 400, so it IS a leap year.