all comes down to detailed questioning, in order to know what the people are capable of; one method is a checklist of ADL's (Activities of Daily Living): https://www.ncbi.nlm.nih.gov/books/NBK470404/

the trick is to make the questioning sound like a casual conversation; "getting old (i.e. in chronological years)" is not a valid excuse - traditionally the older ladies and gentlemen were the wiser members of the tribe; inflation makes our elders consume garbage, unknowingly or ignorantly