Exxon is inquiring about the age of job applicants for positions posted in the U.S. They’re doing this by asking about the citizenship of the applicant (irrelevant to the posted requisition), then asking what year citizenship was acquired, instructing the applicant to fill in their birth date if they were born in the country where the requisition is posted, in this case the U.S.
It looks like they’re using this to pick and choose applicants based on their age, otherwise known as age discrimination.