elderly不可数。elder指较年长的，特别是用于比较家庭成员，但不可与than连用，只用于修饰名词。elderly是委婉用语，意为上了年纪的，外国人一般不说old man，而用elderly man代替，the elderly泛指老人。

例句

A deputation of elders from the village arrived headed by its chief.

村里的`长者代表团在村长的带领下到达了。

'Oi,shut your mouth and have respect for elders,'Langda said to the boy.

“喂，闭嘴，对长者要尊重，”兰达对那男孩说。

He is her elder by several years.

他比她年长几岁。