You use elderly as a polite way of saying that someone is old.
old
young
There was an elderly couple on the terrace.
露台上有一对上年纪的老人。
Typical symptoms of pneumonia may be less prominent in elderly patients.
肺炎的典型症状在老年病人中可能并不明显。
Many of those most affected are elderly.
受影响最大的人中很多是老年人。
The elderly are people who are old.
The elderly are a formidable force in any election.
在任何选举中,老年人都是一股强大的力量。