80 years asked her son to co-sign the lease

[Huiping S.]

One 80 years old applicants' income is not qualified for one property of us. She didn't show up on the viewing (should not let this happen) and asked her son come. Didn't check her credit and other information officially yet. Now she asked her son (in another state) to co-sign for this lease when I declined her. Never did this before. 

My understanding is parents co-sign for colleague kids.

Can I consider co-sign this applicant: elderly and adult son? 

Her son is living in another state. If move forward, I think need to check his background and income and need to consider his income for his living and then his mom's.

Can anybody share some experience?

Thanks!

Huiping