Your birth date is usually put on an employment or grant application, along with where you were born, simply because people need to know if you are a citizen . Actually, if you are tender about your age (and older women, in particular, have a much harder time securing academic employment, despite ageism legislation, so you might be), you can just put where you were born. If you are foreign born you need to indicate whether or not you are a US citizen and, if not, what kind of visa (and its number) as this is essential information for a prospective employer or donor to your research well being.