Offensive and patronising. I find the very description of older women, with or without grandchildren as 'grannys' offensive. It is fine as a name within a family circle, but as a generic, unacceptable.
Cliched, shows only very elderly and mainly disabled women. 'Grandmothers come all shapes and sizes and there are plenty who even in old age are upright fit and well
I am getting more and more angry about the way being old is being equated with being disabled. Nowadays to be the first is to be assumed to bethe second. There are old people and there are disabled people and there is a big overlap, but not big enough to consider the terms synonymous.