I wonder if I can use "the elderly", by which I mean old people, to refer to a specific group of old people. For example:
The elderly with death anxiety
Is this acceptable? Or should I use something like old people with death anxiety instead?
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Sign up to join this communityThe phrase the elderly is absolutely acceptable. In fact, I'd say, given your two options, it's preferred.
The term old people can be interpreted as impolite or disrepectful, especially in more contemorary usages.
If the elderly seems too formal for your particular use, I'd recommend older people instead of old people; that softer wording seems more thoughtful and less inconsiderate:
older people with death anxiety
Interesting Ngram here, if you care to look. It shows how older and elderly began to gain traction in the 1970s and old people began to dip about about decade later:
That said, you've given a very small sample of text, so it's hard to say for sure. Are you making a speech, writing a report, or talking among friends? And what is the surrounding context?
I ask those questions because it is possible to use "old people" without sounding impolite. However, safer alternatives are available.
I managed to find one book that poked fun at this in a humorous way (even the title of the book reveals how this is intended to be humorous):
The only way we can remember how things used to be is by going to museums. Fortunately, we have the Old People. The Old People are our museums.
The Old People who hate being called Old People and prefer to be called Elders, Retirees, or Wise Ones still know how to display the full panoply of emotions...
Source: The Get-Over-Yourself Self-Help Book and Other Essays: The Collected Works of a Misunderstood Curmudgeon
by Sylvia Shawcross