The medical/clinical perspective:
Aging is part of life, old age is a gift visited on comparatively few.
Skin generally loses its turgor (part of why wrinkles appear); mucous membranes thin, dry, and are prone to fissures (cracks). Hair whitens and thins in some areas, and becomes coarse (men's ears, for example) in others.
The atrophic changes in skin and mucous membranes cannot be stopped but they can be slowed. Moisturizer and (for mucous membranes) lubricant becomes important. Women who have been prescribed systemic hormone replacement therapy will have slower atrophy. Women who choose not to use systemic hormone replacement therapy, or are not candidates for that therapy due to another medical condition may benefit from local/topical estrogen therapy. This comes on two forms: estrogen cream and the Estrace vaginal ring. Our clinical experience: women prefer the ring as more convenient and less messy. It does not interfere with sex and needs to be (self-)removed and replaced with a fresh ring roughly every 90 days.
Clitoral tissues can also atrophy, disuse plays a part. Stimulation to orgasm has all sorts of health benefits, especially for seniors--more restful sleep, antidepressant, maintenance of endogenous hormone levels. While health issues and their treatments can change and even interfere with human sexual responsiveness and responses, atrophy is often the consequence of a perception ("too old for sex") than reality.
Maintenance of sexual anatomy and physiology through senior years starts with "use it or lose it".