I think the point is that elderly people are fairly sentient so you don't have to worry about them doing dumb things like darting out in front of a semi truck like you do with kids so there's no reason to warn drivers about a high density of them since they behave like normal pedestrians if perhaps a bit slower.

I think it's more to warn a motorist to be mindful of slow moving people. And older people do occasionally fall over too.

Naples FL needs signs like these. Only it’s to warn motorists of elderly people attempting to pilot Lamborghinis and other ridiculously powerful sports cars. It’s surreal to see valet have to help an 80 year old out of a aventador and the step up the curb to the door of a restaurant.