老衰【ろうすい】
senility, senile decay, infirmity (through age)
衰弱【すいじゃく】
weakness, debility, breakdown, prostration
衰える【おとろえる】
to become weak, to decline, to wear, to abate, to decay, to wither, to waste away
盛衰【せいすい】
rise and fall, ups and downs, welfare, vicissitudes