AP Style holds that you should use this word carefully and sparingly. Do not refer to a person as elderly unless it is clearly relevant to your story.
It is appropriate in generic phrases that do not refer to specific individuals. For example,
- Concern for the elderly
- A home for the elderly
If the intent is to show that an individual’s faculties have deteriorated, cite a graphic example and give attribution for it. Use age when available appropriate.
Apple this same principle to terms such as “senior citizen.”