Ageing and getting frail with overarching fear of losing control. Can it cause mental changes?

Yes. Always will. The stage you refer to is the final fear: dying. In the past month, I have celebrated the birth and life of two of my pts: elderly italian, proud women with a spark in their eyes. One is 101, the other ten years her senior! One of the giants in geriatric medicine (and colleague at hopkins) described aging as 'homeostenosis': all narrows & stiffens. Letting go is the only way of going on. Relax.