Why did the woman lie about her age on FB?

Women lie about their age doesn't hold true always as sometime they are forced to do so. Mrs Joseph, resident of Michigan, was born on April 19, 1908 and joined facebook to remain in touch with her granddaughter. But thanks to Facebook, where they don't accept the birth date upto certain years. Writing in the about section on her Facebook page, she says "Facebook wouldn't let me enter in a date that goes back that far".

According to Gail Marlow, Mrs Joseph's granddaughter when she tries inputting her grandmother's birth year as 1908, Facebook changes it to 1928. So for the past two years, her age is 99 on facebook.
Marlow told WDIV-TV she 'would love to see' Joseph's real age displayed on Facebook and chalked up her inability to do so to 'a glitch in the system'.