this is a measure against age discrimination. probably the admission office uses this information to determine an age distribution of their applicants, but i doubt it they use it directly in their admission decisions. from the background of an applicant you can indirectly say something about their age. for instance, one who got his master and then went in the workforce for about 2 years, most likely he/she is about 25 years old. in the US is so common to suddenly change your career so I don't think age matters that much for the admission committee.
lukas, mult noroc