On December 26 1987, Pauline Letlhake gave birth to twins Xolisa and Xolile, but according to the Department of Home Affairs, they were born two years apart.
Letlhake, of Kagiso on the West Rand, said she obtained the correct birth certificates soon after her babies were born.
Things went wrong in 2003 when she applied for new digital birth certificates at the department's office in Johannesburg.
While Xolile's new document reflected the correct date of birth, Xolisa's stipulated she was born in 1989.
Letlhake reported the error and was referred to the Orlando West office, which did not help. She then went to the Krugersdorp branch. Here, Xolisa was asked to fill in forms to rectify the error so that she could apply for an ID.
But Xolisa is still waiting for her ID five years later.
Xolile got his ID in 2006.
Home Affairs spokesman Mantshele Tau said: "The process of helping Xolisa is just about to be finalised, but we will also investigate why it took so long for her to get her correct birth certificate and ID."