elderly
You use elderly as a polite way of saying that someone is old.上年纪的
So "elderly" is a formal and written term to describe people who are old.是书面和正式的用语,表示礼貌
There was an elderly couple on the terrace.
露台上有一对上年纪的老人.
old people
It is a general phrase to describe people who are old.普通用语,表示老年人可以更详细一点吗？不知道还要怎么详细。一个书面用语一个普通用语。