What is the best way to handle anger / rage in the elderly? (not related to dementia or alzheimer's)

Oddly enough: You might be surprised to hear that it could be poor diet! emotional reflexes are controlled by the lower part of the brain and if oxidation (the equivalent of combustion of fuel) is compromised by an excess of empty calories (food wirhout vitamins) that part of the brain becomes irritable and emotional reactions become excessive.

Divert attention: Attentive listening for a few minutes, empathy if appropriate. However, if it is anger over an issue where a suggestion of how to deal with it will be useless [the yes but people], then if appropriate validate the emotion but then try to shift attention to something that the person enjoys. For many people offering solutions is useless and frustrating for all involved. Empathy works but change topic.

Depends: First focus on safety for all, then one needs a full assessment to determine possible causes then treatment strategies can be pursued. A geriatric psychiatrist or behavioral neurologist may be able to help.