of, exhibiting, or characteristic of old age, or the mental or physical weakness associated with it
No trace of the rifle's deadly work could be found on the tiger … Evidently the beast of prey had succumbed to heart-failure, caused by the sudden report of the rifle, accelerated by senile decay — Saki
senility /siʹniliti/ noun
[Latin senilis, from sen-, senex old, old man]