Pretty much without exception they're going to have much more delicate skin & very brittle nails.
That's aside from the high instances of corns, bunions, hammertoe, arthritis, calluses, blood thinning meds for heart conditions/strokes & circulatory problems. Endless contraindications.
There is a skill and technique in dealing with elderly feet. Perhaps a layperson, such as a potential oap client, would not be aware of this and would therefore think it appropriate. But a professional should be aware they are high risk and require additional skills that the vast majority of beauty therapists don't hold. It's an ethical no go in my books.