Abnormal or unpleasant odors may be caused by diseased or necrotic tissue in the respiratory or upper gastrointestinal tracts, including mouth and nasal cavity. Diseased teeth are a common cause in dogs and cats. In addition, certain metabolic diseases may produce distinctive breath odor, e.g. ketoacidosis, uremia.
Practically elderly is a person who needs special consideration due to advanced age. Which can happen in late 50s or in late 80s. If he or she can punch your lights out for calling them elderly, and you cannot run from them either, they possibly aren't.
The US Census bureau defines elderly as 65+, and most other US Government programs use this definitition, with the notable exception of Older Americans Act programs, which define elderly as 60+. (Most adults I know over the age of 60 or 65 prefer not to use the word elderly at all, with any age range definition.)