Would you say describing somebody as "geriatric" is offensive? I think it's neutral in American English, but the Oxford Advanced Learner's Dictionary describes it as "informal" and "offensive".
Since geriatric is defined as
I would imagine that it might be a bit offensive to the many healthy seniors who might be lumped into that category.
I think a much less loaded term is senior, widely accepted to include anyone 65 and over.
The book Agewise: Fighting the New Ageism in America by Margaret Morganroth Gullette supports this to some degree.
The OED’s first definition of geriatric is:
Geriatrics is ‘the branch of medicine, or of social science, dealing with the health of old people.’ The -iatrics part is from the Greek word for ‘physcian’.
The OED’s second definition is:
It will not always be offensive, and may sometimes, indeed, be humorous. But unless you are sure that you are using it in an appropriate context, it might be best to avoid it.
Some words which start off as entirely medical terms, become pejorative and unpleasant as people (often beginning with kids in playgrounds), use them as terms of derision.
Classically in this category is 'Spastic', which originated as a medical term to describe certain types of cerebral palsy. But it became a word for referring derisively to anyone who had awkward physical movements. Children who could not compete athletically were often called this by their peers. Members of the crowd at football matches would use it for opposing players, or for the referee. So whilst the word is still used medically in some parts of the world, it is socially proscribed in Britain as offensive.
Unfortunately I do see the possibility of 'geriatric' going the same way. And I speak as one over 65, who if he had to go into hospital might well be put in a ward with that name notwithstanding the fact that I do 15 mile walks on a reasonably regular basis.