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