Income: If either of the applicants is a business, income is NA [Commentary to §1003.4(a)(10)(iii)(#7)]. The wording in the commentary says "when the applicant or co-applicant is not a natural person . . ."
Age: I understand you are to report the age of all natural persons that apply. Therefore, you would give the DOB of the co-borrower. [Commentary to §1003.4(a)(10)(ii)(#4)]
The wording in the Commentary cited is the same ("applicant or co-applicant"). Last year, I wrote the CFPB and asked if "or" meant "if either is a non-natural person are we to report NA?" The CFPB replied that ethnicity, race, sex and age are always reported for people. Income is always NA if there's a entity involved.